The origin, migration, and accumulation mechanism of germanium and the metallogenic model of coal-hosted Ge ore deposits in Wulantuga, Erlian Basin, China

Abstract

To explore the source, migration, and enrichment mechanism of germanium (Ge) and the metallogenic model of the Wulantuga coal-hosted Ge ore deposits in the Shengli Coalfield, this study analyzed the geochemical parameters of Ge-rich coal seams, including major element, trace elements, and rare earth element (REE) compositions, with X-ray fluorescence (XRF) spectrometry, inductively coupled plasma mass spectrometry (ICP-MS) and instrumental neutron activation analysis (INAA). An isoline map of Ge concentration and a cross-section map of sedimentary strata and Ge element distribution were drawn with the sampling data. The results showed that there were three periods of Ge accumulation in the Wulantuga coal seam. The enrichment coefficients of the low-content Ge samples and high-content Ge samples displayed that Ge was enriched together with As, Mo, Sb, and W. Compared with the Ge-bearing parent rocks located southwest of the Wulantuga area, the Ge-rich samples are clearly enriched in heavy REEs relative to light REEs in the REE distribution pattern, with positive anomalies of Tb, Ho, Tm, (La/Yb)n and (La/Sm)n > 1, as well as a very high positive δEu anomaly, which indicated that the Ge ore deposit in Wulantuga was indeed likely affected by hydrothermal fluids with a left-slanting REE distribution pattern. In addition, based on the sulfophilic affinity and organic affinity of Ge and the geochemical characteristics of Ge in hydrothermal fluids, the authors speculate that the Ge-rich fluids originated from thermal convection and the interaction between surface freshwater carrying O2 and hydrothermal fluids from the mantle.