Consistent trace element distribution and mercury isotopic signature between a shallow buried volcanic-hosted epithermal gold deposit and its weathered horizon

Abstract

Trace elements and Hg isotopic composition were investigated in mineralized rocks, barren rocks, and mineral soils in the Xianfeng prospect, a shallow buried epithermal gold deposit in northeastern China, to understand whether this deposit has left a diagnostic geochemical fingerprint to its weathered horizon. All the rocks and soils display congruent patterns for immobile elements (large ion lithophile elements, high field strength elements, and rare earth elements), which reflect the subduction-related tectonic setting. Both mineralized rocks and soils showed common enrichment of elemental suite As -Ag-Sb-Hg, suggesting that the Xianfeng gold deposit has released these elements into its weathered horizon. Similar mercury isotopic composition was observed between mineralized rocks (delta Hg-202: -0.21 +/- 0.70 parts per thousand; Delta Hg-199: -0.02 +/- 0.12 parts per thousand; 2SD) and barren rocks (delta Hg-202: -0.46 +/- 0.48 parts per thousand;Delta Hg-199: 0.00 +/- 0.10 parts per thousand; 2SD), suggesting that mercury in the Xianfeng deposit is mainly derived from the magmatic rocks. Mineralized soils (delta Hg-202: -0.44 +/- 0.60 parts per thousand; -0.03 +/- 0.14 parts per thousand; 2SD) and barren soils (delta Hg-202: -0.54 +/- 0.68 parts per thousand; Delta Hg-199: -0.05 +/- 0.14 parts per thousand; 2SD) displayed congruent Hg isotopic signals to the underlying rocks, suggesting limited Hg isotope fractionation during the release of Hg from ore deposit to soils via weathering. This study reveals evidence of a simple and direct geochemical link between this shallow buried hydrothermal deposit and its weathered horizon, and highlights that the weathering of shallow-buried hydrothermal gold deposits can release a substantial amount of heavy metals (e.g. Hg, As and Sb) to surface soil. (C) 2020 Elsevier Ltd. All rights reserved.