Mineralogical and geochemical compositions of the Pennsylvanian coal in the Adaohai Mine, Daqingshan Coalfield, Inner Mongolia, China: Modes of occurrence and origin of diaspore, gorceixite, and ammonian illite

[International Journal of Coal Geology 94 (2012) 250–270]

Abstract:The Late Permian coal in the Fusui Coalfield of southern China is characterized by high Fe-sulfide and organic sulfur contents (2.60 and 2.94%, respectively). Trace elements including Zr (354 μg/g on average), Hf (9.18 μg/g), Y and rare earth elements (REY, 302 μg/g), Li (97.9 μg/g), and Cs (7.02 μg/g) are significantly enriched in these coals. In addition to Hg and Se enrichment in the roof and floor of the coal, fluorine, Mo, and U are enriched in the roof; the floor is rich in Cl, S, Fe, Pb, and Cd. Compared to the upper continental crust, REY in the parting and coal bench samples are characterized by heavy-REY and light-REY enrichment, respectively; the coals, partings, and host rocks (roof and floor) have negative Eu anomalies. The coal benches have higher ratios of U/Th, Yb/La, Nb/Ta, and Zr/Hf, and more abundant heavy rare earth elements than their adjacent partings. These geochemical anomalies are attributed to the composition of terrigenous materials derived from the Yunkai Upland, multi-stage (syngenetic and epigenetic) hydrothermal fluid activities, and intensive leaching and re-distribution of lithophile elements from partings to the underlying coal benches. Both the organic and sulfide sulfur are also derived mainly from the hydrothermal fluids rather than the marine influence. Theminerals in the samples studied, including kaolinite, quartz, and REE-bearing minerals, are of both terrigenous and hydrothermal origin. Al-oxyhydroxides, crystalline FeSO4(OH), water-bearing Fe-oxysulfate, and goyazite were derived from the hydrothermal activity. Kaolinite, quartz, REE-bearing minerals, and apatite from the sediment source region were also subjected to destruction by hydrothermal fluid leaching.

Mineralogical and geochemical anomalies of late Permian coals from the Fusui Coalfield, Guangxi Province, southern China: Influences of terrigenous materials and hydrothermal fluids

[International Journal of Coal Geology 105 (2013) 60–84]

Abstract:The Lincang Neogene high-Ge coal deposit in Yunnan, southwestern China, is one of the major coal-hosted Ge deposits in the world. This study reports new data on the petrological, mineralogical, and geochemical compositions of 57 samples (including coal bench samples, roofs, floors, partings, and batholith granite) of three high-Ge coal seams (S3, Z2, and X1) from the Dazhai Mine, Lincang Ge ore deposit, and provides new insights into the origin and modes of occurrence of the minerals and elements present. The coals have huminite random reflectances in the 0.33–0.48% range. On a mineral-free basis, the coal samples are dominated by huminite-groupmacerals, all having more than 88.5% total huminite. Ulminite and attrinite generally dominate the huminite macerals. Structured inertinite is rare, with funginite being the most abundant inertinite form. The minerals in the coals are mainly composed of quartz, and, to a lesser extent, kaolinite, illite, and mica. A hydrous beryllium sulfate phase (BeSO4·4H2O) is present in the low temperature ashes of several coal samples. Compared to average values for world low-rank coals, beryllium (up to 2000 μg/g and 343 μg/g on average), Ge (up to 2176 μg/g and 1590 μg/g on average), and W (up to 339 μg/g and 170 μg/g on average) are unusually enriched in the Lincang coals, with a concentration coefficient N100 (CC = ratio of element concentration in investigated coals vs. world low-rank coals); elements As (156 μg/g on average), Sb (38 μg/g), Cs (25.2 μg/g), and U (52.5 μg/g) are significantly enriched (10 b CC b 100); niobium (28.2 μg/g) is enriched (CC = 8.55); zinc, Rb, Y, Cd, Sn, Er, Yb, Lu, Hg, Tl, and Pb are slightly enriched (2 b CC b 5). The biotite- and two-mica granites, which served as both the basement for the coal-bearing sequence and as a source of sediment input, were also either hydrothermally-altered or -argillized. The alteration appears to have taken place during or shortly after deposition of the coal-bearing sequence. Two types of metasomatites of hydrothermal origin, including quartz–carbonate and carbonate, were identified, which occur as partings and as roof and floor strata. These metasomatites were formed at the syngenetic or early diagenetic stages of coal deposition. The rare earth elements in these hydrothermal rocks are characterized by a heavy REE enrichment type and by distinct positive Eu anomalies, compared to the upper continental crust. Hydrothermal solutions have played a significant role in producing the elemental and mineralogical anomalies in the Lincang Ge ore deposit. The hydrothermal solutions leaching the batholith granite were a mixture of alkaline N2-bearing and volcanogenic CO2-bearing fluids, which led to the enrichment of trace elements, not only including assemblages of Ge–WandBe–Nb–U (both leached fromgranite and the deposited in the peat), but also As–Sb (from volcanogenic solution), as well as the alteration and argillization of the batholith granites, and the formation of carbonate and quartz–carbonate metasomatites.

Origin of minerals and elements in the Late Permian coals, tonsteins, and host rocks of the Xinde Mine, Xuanwei, eastern Yunnan, China

[International Journal of Coal Geology 121 (2014) 53–78]

Abstract:This paper reports the mineralogical and geochemical compositions of the Late Permian C2 and C3 coals (both medium volatile bituminous coal) from the Xinde Mine, near Xuanwei in eastern Yunnan, which is located close to the area with the highest female lung cancer mortality in China. The two coals are characterized by high ash yields and low sulfur contents. Three factors, including sediment-source region, multi-stage volcanic ash generation, and multi-stage hydrothermal fluid injections, were responsible for variations in the geochemical and mineralogical compositions of the Xinde coals. Trace elements, including V, Sc, Co, Ni, Cu, Zn, Se, Zr, Nb, Hf, and Ta, are enriched in the coals and were mainly derived from the sediment-source Kangdian Upland region. Major minerals in the samples of coal, roof, floor and non-coal sediment partings include quartz, kaolinite, and chamosite, as well as interstratified illite/smectite and anatase. Chamosite in the coal was derived from reactions between kaolinite and Fe–Mg-rich hydrothermal fluids. However, chamosite in the roof strata was directly precipitated from Fe–Mg-rich hydrothermal fluids or was derived from the alteration of precursor minerals (e.g., biotite) by hydrothermal fluids. Quartz in some samples is very high, especially in the roof strata of the C2 and C3 coal. Such high quartz, along with minor minerals including pyrite, chalcopyrite, sphalerite, calcite, celestite, vanadinite, barite, clausthalite and silicorhabdophane, were derived from multi-stage hydrothermal fluids. The floors of both the C2 and C3 coal seams are fully-argillized fine-grained tuffaceous claystone and the immediate roof of the C2 coal is argillized coarse-grained tuff. The original materials of the floors and roofs of these coal seams were high-Ti alkali basaltic volcanic ashes, as indicated by high TiO2, Nb, and siderophile elements, and the distribution patterns of rare earth elements. Two intra-seam tonstein layers in the C3 coal were identified based on their lateral persistence, mineralogical mode of occurrence and composition, as well as their elemental composition. The tonsteins are dominated by kaolinite, with minor quartz and possibly mixed-layer illite/smectite. Both tonsteins were derived from dacitic magma. The ratios of Nb/Ta, Zr/Hf, and U/Th are much lower in tonsteins than in the adjacent coal benches, which is attributed to the hydrothermal leaching.

Determination of As and Se in coal and coal combustion products using closed vessel microwave digestion and collision/reaction cell technology (CCT) of inductively coupled plasma mass spectrometry (ICP-MS)

[International Journal of Coal Geology 124 (2014) 1–4]

Abstract:Toxic elements arsenic and selenium in coal are of great concern mainly because of their adverse effects on human health during coal combustion. This paper describes the concentration determination of As and Se in coal and coal combustion products (CCPs), performed by collision/reaction cell technology (CCT) of inductively coupled plasma mass spectrometry (ICP-MS; collectively ICP-CCT-MS) after closed vessel microwave digestion. The reagents for 50-mg coal sample digestion are 2-ml 40% (v/v) HF and 5-ml 65% (v/v) HNO3 but for the CCP samples, the reagents include 5-ml 40% HF and 2-ml 65% HNO3. To significantly diminish the argon-based interferences at mass to charge ratios (m/z) 75(40Ar35Cl) and 78 (40Ar38Ar), a heliumand hydrogen mixture was used in the optimized hexapole collision cell. The results showed that CCT technology can effectively diminish the spectral interferences of the Ar-based polyatomic ions 40Ar35Cl and 40Ar38Ar to 75As and 78Se, respectively. The method detection limit of As and Se is 0.024 and 0.095 μg/l, respectively, and their linearity of the calibration curves in the range 0–100 μg/l has a determination coefficient r2 N 0.9999. The determination of As and Se in NIST standard reference materials of coal and fly ash samples showed that ICP-CCT-MS plus closed vessel microwave digestion is a reliable method for concentration determination of the two elements in coal and CCPs.