Distribution of Trace Elements in Fractions after Micronization and Density-Gradient Centrifugation of High-Ge Coals from the Wulantuga and Lincang Ge Ore Deposits in China

The Wulantuga (Inner Mongolia) and Lincang (Yunnan Province) germanium ore deposits in China are both considered world-class, coal-hosted Ge deposits. For this paper, two bench coals (WLTG C6-2 from Wulantuga and LC S3-6 from Lincang) were selected to characterize the associations between density fractions (thaceral concentrates) and trace elements using micronization, density-gradient centrifugation (DGC), and inductively coupled plasma mass spectrometry (ICP-MS), especially for the abnormally enriched trace elements (including Ge, W, As, Sb, Be, U, and Nb) and rare earth elements and yttrium (REY) in the Wulantuga and/or Lincang high-Ge coals that are widely considered to have varying degrees of organic affinity. Huminite and inertinite contents of WLTG C6-2 account for 58.4% and 40.7%, respectively, whereas LC S3-6 is dominated by huminite (98.7%). Lower peak densities for huminite/inertinite and Gaussian distributions of DGC profiles after HCl-HF demineralization suggest that some minerals still exist in the micronized fractions. Many trace elements that are typically thought to have organic affinities decrease significantly after HCl-HF demineralization suggesting a mode of occurrence that is susceptible to acid leaching (i.e., weakly bonded to organic matter). In the Wulantuga high-Ge coal, Be and As are preferentially enriched in inertinite-rich density fractions, perhaps due to association with minerals in the heavier fractions. Higher Ge contents are seen in huminite fractions relative to inertinite, possibly due to differences in sites capable of holding Ge. Antimony is slightly more enriched in huminite-rich fractions. A positive Ge W correlation and variable W concentrations across the density profile suggest a mixed organic inorganic affinity for W, and Nb shows a similar distribution to W. Barium is predominantly associated with minerals. In the Lincang S3 seam, Ge concentration increases versus fraction density, probably due to the availability of more bonding sites in denser huminite macerals. The preferential enrichments of Be, U, and Sb in heavier fractions could be due to more bonding sites in denser huminites and/or their inorganic affinities. Arsenic content generally varies smoothly across DGC fractions, and most pyrite particles where at least part of the As occurs were removed in the DGC process. Tungsten, Nb, and possibly Th may occur in similar phases due to their comparable variation trends. In addition, REY anomalies in some fractions mainly result from elevated LREY, and REY (especially LREY) in WLTG C6-2 and LREY in LC S3-6 may occur in minerals with some trace elements, including Sc, Sr, and Ba.