Enrichment of U–Se–Mo–Re–V in coals preserved within marine carbonate successions: geochemical and mineralogical data from the Late Permian Guiding Coalfield, Guizhou, China

Miner Deposita (2015) 50:159–186

Abstract：We present multi-element data on the super-high organic-sulfur (SHOS; 5.19 % on average) coals of Late Permian age from Guiding, in Guizhou Province, China. The coals, formed on restricted carbonate platforms, are all highly enriched in S, U, Se, Mo, Re, V, and Cr, and, to a lesser extent, Ni and Cd. Although the Guiding coals were subjected to seawater influence, boron is very low and mainly occurs in tourmaline and mixed-layer illite/smectite. Uranium, Mo, and V in the coal are mainly associated with the organic matter. In addition, a small proportion of the U occurs in coffinite and brannerite. The major carrier of Se is pyrite rather than marcasite. Rhenium probably occurs in secondary sulfate and carbonate minerals. The U-bearing coal deposits have the following characteristics: the formation age is limited to Late Permian; concentrations of sulfur and rare metals (U, Se, Mo, Re, V, and in some cases, rare earth elements and Y) are highly elevated; the U-bearing coal beds are intercalated with marine carbonate rocks; organic sulfur and rare metals are uniformly distributed within the coal seams; and the combustion products (e.g., fly and bottom ash) derived from the coal deposits may have potential economic significance for rare metals: U, Se, Mo, Re, V, rare earth elements, and Y.

Geochemical and mineralogical evidence for a coal-hosted uranium deposit in the Yili Basin, Xinjiang, northwestern China

Ore Geology Reviews 70 (2015) 1–30

Abstract:The petrological, geochemical, and mineralogical compositions of the coal-hosted Jurassic uranium ore deposit in the Yili Basin of Xinjiang province, northwestern China, were investigated using optical microscopy and field emission-scanning electron microscopy in conjunction with an energy-dispersive X-ray spectrometer, as well as X-ray powder diffraction, X-ray fluorescence, and inductively coupled plasma mass spectrometry. The Yili coal is of high volatile C/B bituminous rank (0.51–0.59% vitrinite reflectance) and has a medium sulfur content (1.32% on average). Fusinite and semifusinite generally dominate the maceral assemblage, which exhibits forms suggesting fire-driven formation of those macerals together with forms suggesting degradation of wood followed by burning. The Yili coals are characterized by high concentrations of U (up to 7207 μg/g), Se (up to 253 μg/g), Mo (1248 μg/g), and Re (up to 34 μg/g), as well as As (up to 234 μg/g) and Hg (up to 3858 ng/g). Relative to the upper continental crust, the rare earth elements (REEs) in the coals are characterized by heavy or/and medium REE enrichment. The minerals in the Yili coals are mainly quartz, kaolinite, illite and illite/smectite, as well as, to a lesser extent, K-feldspar, chlorite, pyrite, and trace amounts of calcite, dolomite, amphibole, millerite, chalcopyrite, cattierite, siegenite, ferroselite, krutaite, eskebornite, pitchblende, coffinite, silicorhabdophane, and zircon. The enrichment and modes of occurrence of the trace elements, and also of the minerals in the coal, are attributed to derivation from a sediment source region of felsic and intermediate petrological composition, and to two different later-stage solutions (a U–Se–Mo–Re rich infiltrational and a Hg–As-rich exfiltrational volcanogenic solution). The main elements with high enrichment factors, U, Se, As, and Hg, overall exhibit a mixed organic–inorganic affinity. The uranium minerals, pitchblende and coffinite, occur as cavity-fillings in structured inertinite macerals. Selenium, As, and Hg in high-pyrite samples mainly show a sulfide affinity.

Elemental and mineralogical anomalies in the coal-hosted Ge ore deposit of Lincang, Yunnan, southwestern China: Key role of N2–CO2-mixed hydrothermal solutions

International Journal of Coal Geology 152 (2015) 19–46

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-group macerals, 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.

Coal deposits as potential alternative sources for lanthanides and yttrium

International Journal of Coal Geology 94 (2012) 67–93

Abstract：This paper presents data on widespread abnormal accumulations of lanthanides and yttrium (REY) in many coal deposits worldwide. High REY contents (>0.1%) have been found in coal seams and coal ashes, as well as in the host and basement rocks of some coal basins. For a preliminary evaluation of coal ashes as an REY raw material, not only the abundance but also the individual REY compositions were taken into account in this paper. Three REY distribution patterns for high-REY coal ashes are fixed, with LREY- (LaN/LuN>1), MREY- (LaN/SmNb1, GdN/LuN>1), and HREY- (LaN/LuNb1) enrichment. Four genetic types of REY enrichment in coal basin can be identified: 1) terrigenous type, with REY input by surface waters; 2) tuffaceous type, connected with falling and leaching of acid and alkaline volcanic ash; 3) infiltrational or meteoric ground water driven type, and 4) hydrothermal type, connected with ascending flows of thermal mineral water and deep fluids. It is shown that the main modes of REY occurrence in high-REY coals are in fine-grained authigenic minerals (REY-bearing aluminum phosphates and sulfates of the alunite supergroup, water-bearing phosphates and carbonates) and organic compounds. Stratabound and cross-cutting REY mineralization may occur in the host and basement rocks of some coal basins. There are tuffaceous and hydrothermal types of REY mineralization outside coal seams that are significantly different in geological settings, ore body shapes, and ore compositions, as well as in REY contents and distribution patterns. The data presented indicate that coal deposits should be regarded as promising objects for recovery of REY as economic by-products of coal mining and combustion. As REY are crucial metals for alternative power and energy-efficient technologies, identification of these resources during coal exploitation and utilization may not only increase beneficiation of coal deposits themselves but also will promote humanity's further movement on the “green road”.

Geochemistry of trace elements in Chinese coals: A review of abundances, genetic types, impacts on human health, and industrial utilization

International Journal of Coal Geology 94 (2012) 3–21

Abstract: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 (ΣLa-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.