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Duan P.,China University of Mining and Technology | Wang W.,China University of Mining and Technology | Liu X.,Yunnan Institute of Coal Geology Prospection | Qian F.,China University of Mining and Technology | And 2 more authors.
International Journal of Coal Geology | Year: 2017

A Lopingian coal from the Reshuihe Mine in southwestern China contains high pyritic sulfur (5.2%) and trace elements including As (10.8 μg/g), Hg (0.81 μg/g), V (98.9 μg/g), Co (15.7 μg/g), Cu (47.5 μg/g), Se (4.8 μg/g) and Th (7.2 μg/g). The variation of trace elements in coal samples of different size and density were investigated. The results showed that the vertical variation of As and Hg through the seam section is the result of hydrothermal activity. Arsenic and Hg are highly concentrated in coal layers far from the parting, roof and floor in vertical section. For example, the highest concentrations of As (44.3 μg/g) and Hg (2.8 μg/g) occur in ply 6, which is 40-cm vertically away from partings. Elements As, Hg, Co, Ni, Se, Sb and Tl occur mainly in pyrite; Be, F, Cs, Th and U are evenly distributed in clay minerals and organic components; V and Cr mainly occur in the organic portions of the coal. The As and Hg content generally increases with greater particle size and density, with content in the light fractions as low as 1.1 and 0.14 μg/g, respectively, and as high as 75.8 and 3.8 μg/g, respectively, in heavy fractions. Co, Ni, Se, Sb and Tl exhibit similar density dependence. Vanadium and Cr are more concentrated in lower-density fractions. The genetic type and mode of occurrence of elements in coal both exert a great impact on their removability; epigenetic and coarse minerals may be readily liberated by gravity separation. Elements associated with pyrite (e.g., As, Hg, Co, Ni, Cu, Se, Sb and Tl) demonstrate high removability; F, Th, U, V and Cr, which mainly occur in clay minerals and/or organic components of the coal, show a relatively low removability. Trace elements in particle size fractions 6–13 mm and < 0.5 mm are most easily removed by gravity separation. In order to fully remove toxic elements from coal, it is suggested fractions with particle sizes of 3–6 mm and 0.5–3 mm be reduced in size to < 0.5 mm prior to gravity separation. © 2017 Elsevier B.V.

Zhao L.,China University of Mining and Technology | Zhao L.,University of New South Wales | Dai S.,China University of Mining and Technology | Graham I.T.,University of New South Wales | And 5 more authors.
Ore Geology Reviews | Year: 2017

A previous study briefly described the occurrence of a new type of Nb(Ta)-Zr(Hf)-REY-Ga (REY: rare earth elements and yttrium) polymetallic mineralization in eastern Yunnan, southwest China. In this paper, the mineralogical and geochemical features have been further advanced through a study of two regionally extensive and relatively flat-lying mineralized layers from No. XW drill core. The layers are clay-altered volcanic ash and tuffaceous clay, and are dominated by clay minerals (mixed layer illite/smectite, kaolinite, berthierine, and chamosite); with lesser amounts of quartz and variable amounts of anatase, siderite and calcite; along with trace pyrite, barite, zircon, ilmenite, galena, chalcopyrite, and REE-bearing minerals. The mineralized samples have higher Al2O3/TiO2 values (13.7–41.4) and abundant rare metal elements (Nb, Ta, Zr, Hf, REE, Ga, Th, and U) whereas less mineralized samples are rich in V, Cr, Co, and Ni and have lower Al2O3/TiO2 values (2.32–7.67). The mineralized samples also have strong negative δEu in chondrite-normalized REE patterns. Two processes are most likely responsible for the geochemical and mineralogical anomalies of the mineralized samples: airborne volcanic ash and multi-stage injection of low-temperature hydrothermal fluids. Based on paragenetic analysis, this polymetallic mineralization is derived from the interaction between alkaline volcanic ashes and subsequent percolation of low-temperature fluids. The intense and extensive alkaline volcanism of the early Late Permian inferred from this study possibly originated from the coeval Emeishan large igneous province (ELIP). This unique Nb(Ta)-Zr(Hf)-REE-Ga mineralization style has significant economic and geological potential for the study of mineralization of the lowest Xuanwei Formation. © 2016 Elsevier B.V.

Dai S.,China University of Mining and Technology | Wang X.,China University of Mining and Technology | Chen W.,China University of Mining and Technology | Li D.,Chongqing Institute of Geology and Mineral Resources | And 8 more authors.
International Journal of Coal Geology | Year: 2010

The No. 12 Coal (Late Permian) in the Songzao Coalfield, Chongqing, southwestern China, is characteristically high in pyrite and some trace elements. It is uniquely deposited directly above mafic tuff beds. Samples of coal and tuffs have been studied for their mineralogy and geochemistry using inductively coupled plasma-mass spectrometry, X-ray fluorescence, plasma low-temperature ashing plus powder X-ray diffraction, and scanning electron microscopy equipped with energy-dispersive X-ray analysis.The results show that the minerals of the No. 12 Coal are mainly composed of pyrite, clay minerals (kaolinite, chamosite, and illite), ankerite, calcite, and trace amounts of quartz and boehmite. Kaolinite and boehmite were mainly derived from sediment source region of mafic tuffs. Chamosite was formed by the reaction of kaolinite with Fe-Mg-rich fluids during early diagenesis. The high pyrite (Sp,d=8.83%) in the coal was related to marine transgression over peat deposits and abundant Fe derived from the underlying mafic tuff bed. Ankerite and calcite were precipitated from epigenetic fluids.Chemical compositions of incompatible elements indicate that the tuffs were derived from enriched mantle and the source magmas had an alkali-basalt character. Compared to other coals from the Songzao Coalfield and common Chinese coals, the No. 12 Coal has a lower SiO2/Al2O3 (1.13) but a higher Al2O3/Na2O (80.1) value and is significantly enriched in trace elements including Sc (13.5μg/g), V (121μg/g), Cr (33.6μg/g), Co (27.2μg/g), Ni (83.5μg/g), Cu (48.5μg/g), Ga (17.3μg/g), Y (68.3μg/g), Zr (444μg/g), Nb (23.8μg/g), and REE (392μg/g on average). Above mineralogical compositions, as well as similar ratios of selected elements (e.g., SiO2/Al2O3 and Al2O3/Na2O) and similar distribution patterns of incompatible elements (e.g., the mantle-normalized diagram for incompatible elements and chondrite-normalized diagram for rare earth elements) of coal and tuff, indicated that enriched trace elements above were largely derived from mafic tuffs, in addition to a minor amount from the Kandian Oldland. © 2010 Elsevier B.V.

Dai S.,China University of Mining and Technology | Wang X.,China University of Mining and Technology | Zhou Y.,Yunnan Institute of Coal Geology Prospection | Hower J.C.,University of Kentucky | And 4 more authors.
Chemical Geology | Year: 2011

Silicic and alkali intra-seam tonsteins were discovered earlier in southwestern China. This paper reports new data on the geochemical and mineralogical compositions of tonsteins from the Songzao Coalfield, Chongqing, southwestern China, and provides new insights into the origin and distribution of the minerals and elements present. Three types of tonsteins (silicic, mafic, and alkali) were identified based on their lateral correlation over a large coalfield area and the overall similarity of corresponding mineralogical and chemical compositions. The clay minerals in most tonsteins of different sources and the mafic tuffs in the lower portion of the late Permian are dominated by kaolinite or are mainly composed of mixed layers of illite and smectite. The silicic tonsteins contain high quartz while the mafic tonsteins and mafic tuffs have high contents of anatase. All the tonsteins and tuffs contain pyrite, attributed to the seawater influences. The mafic tonsteins and tuffs have higher pyrite contents, probably due to the higher Fe derived from mafic volcanic ashes. The mafic tonsteins and tuffs are enriched in Sc, V, Cr, Co, and Ni, similar to the normal clay sediments in the southwestern China, indicating similar sources. The alkali tonsteins are characterized by high contents of Nb, Ta, Zr, Hf, REEs (rare earth elements), and Ga. The TiO2/Al2O3 values are 0.02-0.08 for alkali, <0.02 for silicic, and >0.10 for mafic tonsteins and mafic tuffs, indicating different magma sources. Mafic tuffs and alkali tonsteins are enriched in rare earth elements, and silicic tonsteins contain a lowest REE but have the highest fractionation between light REE and heavy REE. Tonsteins and tuffs may be at the periphery of the Emeishan Large Igneous Province and probably resulted from a waning activity of the plume. They were probably derived from different mantle sources that were underwent not only low-degree partial melting but also fluid fractionation and contamination by lithospheric mantle. Their source magmas had an alkali-basalt composition and were similar to that of ocean island basalt. © 2010 Elsevier B.V.

Dai S.,China University of Mining and Technology | Ren D.,China University of Mining and Technology | Chou C.-L.,Illinois State Geological Survey | Finkelman R.B.,University of Texas at Dallas | And 2 more authors.
International Journal of Coal Geology | Year: 2012

China will continue to be one of the largest coal producers and users in the world. The high volume of coal use in China has focused attention on the amounts of toxic trace elements released from coal combustions and also the valuable trace elements extracted or potentially utilized from coal ash.Compared to world coals, Chinese coals have normal background values for most trace elements, with the exception of higher Li (31.8. μg/g), Zr (89.5. μg/g), Nb (9.44. μg/g), Ta (0.62. μg/g), Hf (3.71. μg/g), Th (5.84. μg/g), and rare earth elements (∑. La-Lu. +. Y, 136. μg/g). This is not only due to the higher ash yields of Chinese coals but also to alkali volcanic ashes found in some southwestern coals. The background values of toxic elements of Hg (0.163. μg/g), As (3.79. μg/g), and F (130. μg/g) in Chinese coals are comparable to coals from most other countries.The genetic types for trace-element enrichment of Chinese coals include source-rock- controlled, marine-environment-controlled, hydrothermal-fluid-controlled (including magmatic-, low-temperature-hydrothermal-fluid-, and submarine-exhalation-controlled subtypes), groundwater-controlled, and volcanic-ash-controlled. The background values of trace elements were dominated by sediment source regions. Low-temperature hydrothermal fluid was one of the major factors for the local enrichment of trace elements in southwestern China.Serious human health problems caused by indoor combustion of coal in China include endemic fluorosis, arsenosis, selenosis, and lung cancer. Endemic fluorosis, mainly occurring in western Guizhou, was mostly attributed to the high fluorine in clay that was used as a briquette binder for fine coals, in addition to a small quantity of fluorine from coal. Fluorine in the coal from endemic-fluorosis areas of western Guizhou is within the usual range found in China and the world. Endemic arsenosis in southwestern Guizhou is attributed to indoor combustion of high-As coal. Endemic selenosis in Enshi of Hubei was due to high Se in carbonaceous siliceous rocks and carbonaceous shales. Fine particles of quartz, released into air during coal combustion, are hypothesized as a possible cause for the lung cancer epidemic in Xuanwei, Yunnan, China.Valuable elements, including Ge, Ga, U, REE (rare earth element), Nb, Zr, and Re are concentrated to levels comparable to conventional economic deposits in several coals or coal-bearing strata in China. The Ge deposits at Lincang, Yunnan province and Wulantuga, Inner Mongolia have been exploited and industrially utilized. The enrichment of Ge in the two deposits was caused by hydrothermal fluids associated with adjacent granitoids. The Ga (Al) ore deposit in the Jungar Coalfield, Inner Mongolia, was derived from the neighboring weathered and oxidized bauxite of the Benxi Formation (Pennsylvanian). The Nb(Ta)-Zr(Hf)-REE-Ga deposits in the Late Permian coal-bearing strata of eastern Yunnan and Chongqing of southwestern China were attributed to ashes of the alkali volcanic eruptions. © 2011 Elsevier B.V.

Dai S.,China University of Mining and Technology | Li T.,China University of Mining and Technology | Li T.,Chongqing Institute of Geology and Mineral Resources | Seredin V.V.,RAS Institute of Geology and Mineralogy | And 7 more authors.
International Journal of Coal Geology | Year: 2014

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. © 2013 Elsevier B.V.

Dai S.,China University of Mining and Technology | Seredin V.V.,RAS Institute of Geology and Mineralogy | Ward C.R.,University of New South Wales | Jiang J.,198 Coal Geology Exploration Group | And 9 more authors.
International Journal of Coal Geology | Year: 2014

The fly ashes derived from three giant coal-hosted Ge deposits, Lincang (Yunnan of southwestern China), Wulantuga (Inner Mongolia of northern China), and Spetzugli (Primorye, Russian Far East), are unique because they are highly enriched in elements, including up to (on an organic-free basis): 4.66% Ge, 2.12% As, 1.56% F, 1.22% Sb, 0.56% W, 0.56% Zn, 0.55% Pb, 0.13% Sn, 0.12% Ga, 0.056% Bi, 0.04% Be, 0.028% Cs, 0.017% Tl, and 0.016% Hg. These high element concentrations in the fly ashes are due both to their high levels in the raw coals from which they were derived and their high volatility during the coal combustion process.Rare earth elements and yttrium (REY) were fractionated during coal combustion. They are more enriched in fly ashes than in slag from the respective coals. Maximum REY enrichment may occur either in fine-grained fly ash from baghouse filters or in coarse-grained fly ash from electrostatic precipitators. Cerium and Eu are more enriched in the fly ashes than other REY, and yttrium is relatively depleted in the fly ashes in comparison with the slag.Three types of unburnt carbon can be identified in the fly ashes: (1) carbon with well-preserved initial maceral structures (fusinite and secretinite), (2) isotropic and anisotropic carbon, and (3) secondary fine-grained carbon. The last type of unburnt carbon is characterized by embedded fine-grained Ge-bearing and other mineral phases.Ge oxides (e.g., GeO2) are the major Ge carrier in the fly ashes. Other Ge-bearing mineral phases, however, were also identified, including glass, Ca ferrites, solid solutions of Ge in SiO2, and probably elemental Ge or Ge (Ge-W) carbide, as well as previously-unknown complex oxides including (Ge,As)Ox, (Ge,As,Sb)Ox, (Ge,As,W)Ox, and (Ge,W)Ox. Some portion of the Ge occurs as adsorbed species in different types of unburnt carbon (Types 1 and 2) in the ash particles. © 2013 Elsevier B.V.

Liu J.,China University of Mining and Technology | Yang Z.,Yunnan Institute of Coal Geology Prospection | Yan X.,China University of Mining and Technology | Ji D.,China University of Mining and Technology | And 2 more authors.
Fuel | Year: 2015

Abstract The concentrations and modes of occurrence of highly-elevated trace elements including V, Cr, Se, Mo, Cd, Re, and U in some late Permian coals preserved within marine carbonate successions from Southwest China, were investigated using inductively coupled-plasma mass spectrometry (ICP-MS), sequential chemical extraction procedures (SCEP), field emission-scanning electron microscopy in conjunction with an energy-dispersive X-ray spectrometer (FE SEM-EDS), and X-ray powder diffraction analysis (XRD). The coals present in this study are characterized by superhigh-organic-sulfur, ranging from 5.01% to 9.87%, and by highly-elevated concentrations of V (859 ppm on average), Cr (370 ppm), Se (29.3 ppm), Mo (364 ppm), Cd (3.87 ppm), Re (0.47 ppm), and U (214 ppm). The minerals in the coals are predominantly composed of illite or mixed-layer illite/smectite, which, together with quartz, were derived from sediment-source region. The SCEP results showed that elements V, Cr, Se, Re, U, and Mo are mainly associated with organic matter of the coal, and to a lesser extent, are associated with illite or mixed-layer illite/smectite. Traces of U-bearing minerals (coffinite and brannerite) were identified in the coal. Cadmium is mainly and Cr and Mo are partially distributed in sulfide minerals. A significant proportion of Re is also associated with the carbonate fraction. © 2015 Elsevier Ltd. All rights reserved.

Dai S.,China University of Mining and Technology | Zhou Y.,Yunnan Institute of Coal Geology Prospection | Zhang M.,Yunnan Institute of Coal Geology Prospection | Wang X.,China University of Mining and Technology | And 7 more authors.
International Journal of Coal Geology | Year: 2010

This paper describes a new type of Nb(Ta)-Zr(Hf)-REE-Ga polymetallic deposit of volcanic origin in the late Permian coal-bearing strata of eastern Yunnan, southwestern China. Well logging data (especially natural gamma-ray), geochemical data (high concentrations of Nb, Ta, Zr, Hf, REE, and Ga) and mineralogical compositions (Nb(Ta)-, Zr(Hf)-, or REE-bearing minerals rarely observed), together with the volcanic lithological characteristics indicate that there are thick (1-10m, mostly 2-5m) ore beds in the lower Xuanwei Formation (late Permian) in eastern Yunann of southwestern China. The ore beds are highly enriched in (Nb,Ta)2O5 (302-627ppm), (Zr,Hf)O2 (3805-8468ppm), REE (oxides of La-Lu+Y) (1216-1358ppm), and Ga (52.4-81.3ppm). The ore beds are mainly composed of quartz, mixed-layer illite-smectite, kaolinite, berthierine, and albite. Four types of ore beds in the study area were identified, namely, clay altered volcanic ash, tuffaceous clay, tuff, and volcanic breccia. Preliminary studies suggest that the high concentrations of otherwise rare metals were mainly derived from the alkalic pyroclastic rocks. The modes of occurrence, spatial distribution, and enrichment mechanism of the rare metals, however, require further study. © 2010 Elsevier B.V.

Wang X.,China University of Mining and Technology | Dai S.,China University of Mining and Technology | Chou C.-L.,Illinois State Geological Survey | Zhang M.,Yunnan Institute of Coal Geology Prospection | And 6 more authors.
International Journal of Coal Geology | Year: 2012

This paper describes the mineralogy and geochemistry of a batch of 17 coal samples covering the Late Permian Longtan Formation from a drill core from the Taoshuping mine, eastern Yunnan Province, China. The results show that minerals in the coals include quartz, kaolinite, calcite, chamosite, pyrite, mixed-layer I/S and minor marcasite, siderite, anatase, ankerite, and dolomite. Modes of occurrences of authigenic quartz and chamosite suggest that they were mainly precipitated from Fe-Mg-rich siliceous solution derived from the weathering of Emeishan basalt, which was induced by mantle plume eruption during late Middle Permian and covers most places of southwest China. Kaolinite and mixed layer I/S are mainly of detrital origin. Correspondingly, the elevated trace elements, including V, Cr, Co, and Ni, in the coals are closely related to Emeishan basalt. Trace amounts of detrital calcite, ankerite and siderite in the coals probably originated from the Maokou limestone. The frequent presence of high temperature quartz indicates that felsic volcanic eruption took place through the entire Late Permian Epoch. Mineral matter in the coals was not only derived from Emeishan basalt in the Kangdian Oldland, but also felsic volcanic ashes, mafic volcanic ashes, and limestone of the Maokou Formation. © 2012 Elsevier B.V.

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