Distribution, occurrence and enrichment causes of gallium in coals from the Jungar Coalfield, Inner Mongolia

Abstract

We collected eleven bench samples of No. 6 coal from the Heidaigou Surface Mine, Jungar Coalfield, Inner Mongolia, China, and four samples from the affiliated coal preparation plant. Based on these samples, we used inductively coupled-plasma mass spectroscopy, X-ray diffraction, scanning electron microscope with an energy-dispersive X-ray spectrometer techniques, and borehole exploration data, to investigate the distribution, occurrence and enrichment causes of gallium (Ga) in the coals. Our results show: (1) Gallium is significantly enriched in the coal seams from the study area, with an average content of 18.8-26.0 ppm. Gallium is distributed heterogeneously in the coals, and reaches ore-forming scales only in No. 6 coal of Heidaigou Surface Mine, not in the other mining districts of Jungar Coalfield. (2) On the horizontal plane, Ga is enriched in the main minable coals from the northern and middle part of the coalfield. In the vertical profile, Ga content in the coal seams is higher at the base of Taiyuan Formation (Nos. 8 and 9) and Shanxi Formation (Nos. 3 and 4) than at the top of the Taiyuan Formation. Within the identical coal seam, Ga content is higher in the benches near the roof and floor than in the middle section. (3) Gallium in the coals is associated mainly with kaolinite and boehmite. Additionally, Ga may be adsorbed to some extent by humic acid, resulting in a high level in weathering coal. (4) Geological factors affect Ga enrichment in coal, such as the property of parent rocks in the source area, the sedimentary environment, organic matter, structure, and past magmatic hydrothermal activity. Especially, Ga content in parent rocks plays a leading role. (5) The mobility and precipitation of trace elements like Ga are controlled principally by the geochemical behavior of the major element Al. Terrestrial and transgressive environments can cause the precipitation of bauxite, whereas marine-continental depositional environments may cause the separation of Ga from Al. In addition, Ga may migrate in the form of gas, and may be affected by the ground temperature. Thus, it is relatively enriched in high-volatile coal. coal, gallium, distribution, occurrence, enrichment causes, Jungar Citation:Wang W F, Qin Y, Liu X H, et al. Distribution, occurrence and enrichment causes of gallium in coals from the Jungar Coalfield, Inner Mongolia.

The Petrography, Mineralogy and Geochemistry of Some Cu- and Pb-Enriched Coals from Jungar Coalfield, Northwestern China

“…The Cu content for No.6 coal is higher in Huangyuchuan mine than that in Heidaigou [39] and Haerwusu mine [38], which located in the of north central of Jungar coalfield (Figure 1) [40], at 55 μg/g, 16 μg/g, and 13 μg/g respectively, and it also higher in the No. [33], USC-Unit States Coal [33], HC-Hard coal [30], BC-Brown coal [30].…”

“…6 coal is higher in Huangyuchuan mine than that in Heidaigou [39] and Haerwusu mine [38], which located in the of north central of Jungar coalfield (Figure 1) [40], at 55 µg/g, 16 µg/g, and 13 µg/g respectively, and it also higher in the No. respectively [30,33] (Figure 12), in which the Cu content is much lower than in the crust (60 μg/g) and Pb content is much higher than in the crust (13 μg/g).…”

“…6 coal is situated the north (i.e., moyite from the Yinshan ancient land (Figure 13), and/or the northeast (i.e., Late Palaeozoic Benxi Formation) [38][39][40], while the Proterozoic and Lower Paleozoic granites and sedimentary rocks in the Yinshan area; and probably add some basic volcanic rocks, are terrigenous detrital materials of the No. 4 coal [42].…”

“…The sample site was in the south of the Jungar coalfield with a simple structure in the mining field ( Figure 1), with no fracture development, and Tianjiashipan deflection extension from southwest to northeast with [37][38][39][40][41][42][43][44][45][46][47][48][49] • in the mining field. The formation strike is north by northeast with a gentle dip of 3-5 • inclination angle.…”

Coal deposits as promising alternative sources for gallium

“…However, AAS cannot obtain data for multiple elements simultaneously. In recent decades, inductively coupled plasma mass spectrometry (ICP-MS) has developed rapidly into a reliable and common method for determining trace element concentrations in coal (Dill and Wehner, 1999;Dai et al, 2008Dai et al, , 2012bSpears and Tewalt, 2009;Wang et al, 2011). It has outstanding merits such as high selectivity and sensitivity, and importantly, it has a low detection limit for Ga (0.001 μg/g) (Dai et al, 2006b).…”