Germanium isotopic systematics in Ge-rich coal from the Lincang Ge deposit, Yunnan, Southwestern China

Type Article
Date 2011-07
Language English
Author(s) Qi Hua-Wen1, Rouxel OlivierORCID2, Hu Rui-Zhong1, Bi Xian-Wu1, Wen Han-Jie1
Affiliation(s) 1 : Chinese Acad Sci, Inst Geochem, State Key Lab Ore Deposit Geochem, Guiyang 550002, Peoples R China
2 : IFREMER, UEB, IUEM, Dept Marine Geosci, F-29280 Plouzane, France
Source Chemical Geology (0009-2541) (Elsevier Science Bv), 2011-07 , Vol. 286 , N. 3-4 , P. 252-265
DOI 10.1016/j.chemgeo.2011.05.011
WOS© Times Cited 29
Keyword(s) Germanium, Coal, Stable isotope fractionation, Water-rock interaction, Geochemical tracer
Abstract Organic matter plays an important role in the transport and precipitation of germanium (Ge) in coal-hosted Ge deposits. In this paper. Ge isotopes of coal samples and their combustion products were analyzed in order to investigate the potential use of Ge isotopes as tracers of Ge sources and enrichment mechanisms in coal. Germanium isotopic composition of various samples (mainly Ge-rich lignite) from the Lincang Ge deposit, Yunnan, Southwest China was analyzed using a continuous flow hydride generation system coupled to a Multi Collector Inductively Coupled Plasma Mass Spectrometer (MC-ICP-MS) and the standard-sample bracketing approach. Variations of (74)Ge/(70)Ge ratios are expressed as delta(74)Ge values relative to NIST SRM 3120a Ge standard solution. Ge-rich lignite samples show large Ge isotopic fractionation (delta(74)Ge values range from -2.59 parts per thousand to 4.72 parts per thousand), and their delta(74)Ge values negatively correlate with Ge concentrations. Lignite samples with low Ge concentrations (<500 ppm) tend to show positive delta(74)Ge values, while delta(74)Ge values of lignite samples with high Ge concentrations (>1000 ppm) are close to zero or negative. Along stratigraphic sections, Ge is mainly concentrated in the top or the bottom of the coal seam, such that high values of delta(74)Ge are usually found in the middle part of the coal seam. Interlayered hydrothermal chert and limestone samples in Ge-rich coal seams also show moderate fractionation (delta(74)Ge values range from -0.14 parts per thousand to 2.89 parts per thousand and from 0.55 parts per thousand to 1.87 parts per thousand respectively). The overall variations of delta(74)Ge values of Ge-rich lignite and organic-rich chert samples can be well described by a Rayleigh fractionation model, indicating that preferential enrichment of light Ge isotopes in coal in an open system might be the main factor controlling Ge fractionation in Ge-rich lignite. The germanium isotopic composition of hydrothermal chert (and possibly limestone) might also record the competitive fractionation produced by precipitation of quartz and sorption of coal. Elevated Ge concentrations and/or delta(74)Ge values of some chert, limestone, sandstone, and claystone samples may be attributed to the mixing with Ge-rich organic matter. Furthermore, similar to the fractionation of Zn, Cd and Hg isotopes observed between refinery dust or gas and slag, high temperature coal combustion also fractionates Ge isotopes, with the Ge isotopic compositions of soot being distinctly lighter (up to 2.25 per mil) than those of cinder. The distinct enrichment of potential hazardous elements (i.e., Pb, Cd, and As) and Ge in soot after coal combustion, as well as the common enrichment of Ge in sulfide minerals (e.g. sphalerite), highlights the possibility of using Ge isotopes as useful tracers of sources of heavy metal pollution caused by high temperature industrial processes (coal combustion and Pb-Zn refining) in the environment. (C) 2011 Elsevier B.V. All rights reserved.
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