New data on geology and germanium mineralization in the Hunchun Basin, northeastern China

Abstract

The geochemistry and mineralogy of Palaeogene coals from the Hunchun Coalfield, Jilin Province, northeastern China, have been studied using X-ray fluorescence spectrometry, inductively coupled plasma mass spectrometry, scanning electron microscopy in combination with energy-dispersive X-ray spectrometry, and X-ray diffraction analysis of the low-temperature ash. The 22A Coal from the Banshi Mine is of subbituminous A to high volatile bituminous rank (0.53–0.56% Ro, ran) and has a low sulfur content (0.74% on average). The 22A Coal consists mainly of kaolinite, quartz, illite, and, to a lesser extent, plagioclase, siderite, and pyrite. As compared with the average world low-rank coals, the 22A Coal is enriched in As, Sb, Ge, Cs, and W.Combined with the geochemical features of six other coal seams from the Hunchun Coalfield, the terrigenous materials of the Hunchun coals were dominantly from Mesozoic (mostly Lower Cretaceous) volcanic rocks and Paleozoic granites and associated metamorphic rocks surrounding the coal basin. A minor source was the Paleogene volcaniclastics including some adakitic rocks, which are characterized by higher Sr/Y and La/Yb ratios. The Ge enrichments that are detected in some individual coal benches from the Hunchun Coalfield were related to tectonic uplift of the crystalline rocks surrounding the basin and their following denudation. The oxidized meteoric waters episodically influenced by volcanic-related hot springs might extract Ge from the source rocks and then precipitate it as a result of bio-chemical reduction, forming the mineralization disseminated in the coals.