Textures and trace element signatures of pyrite and arsenopyrite from the Gutaishan Au–Sb deposit, South China

Abstract

The Gutaishan deposit is a slate-hosted lode Au–Sb deposit in the Xiangzhong Sb–Au metallogenic province, South China. The deposit has a proven reserve of ca. 9 -t gold at an average grade of 13-g/t and contains 2500-t Sb. The deposit represents the product of a complex ore-forming process, comprising four different stages, of which the third stage is the main gold–stibnite bearing stage. Scanning electron microscopy, electron probe microanalysis, and laser ablation inductively coupled plasma-mass spectrometry were used to investigate the occurrence of visible gold and the distribution of invisible gold in pyrite and arsenopyrite. Visible gold displays textural complexity with four distinct categories defined and assumed to have formed directly precipitated from ore-forming fluid and remobilized from pyrite and arsenopyrite. Pyrite and arsenopyrite occur as ten and four texturally distinct subtypes; all host invisible gold, which is lattice-bound. Trace element mapping of selected pyrite and arsenopyrite grains reveals a marked compositional zoning with respect to Au and other elements in both minerals. Observed decoupled behavior between Au and As in some grains contradicts the paradigm of coupled Au and As substitution. Evidence suggests that the Gutaishan deposit likely represents an evolving Au–Sb mineralization event recorded by the complex texture and geochemical signatures of visible gold, sulfides, and sulfosalts.