Distribution and formation of variable gold deportment in orogenic gold deposits: A case study of the Huangjindong deposit in the Jiangnan Orogen, China
Zu-Yan Chen, Liang Zhang, David I. Groves, Rong-Hua Li, Ivan Belousov, Qi-Bin Zhang, Si-Chen Sun, Xue Gao, Jia-Le Mu, Li-Qiang YangAbstract
The Huangjindong orogenic gold deposit in the Jiangnan Orogen, China, containing both visible and invisible gold, serves as an ideal research laboratory for a systematic study of gold deportment and its distribution in a single deposit. Minor gold mineralization and hydrothermal alteration occurred during the scheelite-quartz Stage (Quartz-W Stage), marked by the formation of Au- and As-poor pyrite. Gold-sulfides-quartz Stage (Quartz-Au Stage), the major gold stage, involved the preferential deposition of arsenopyrite with adsorption of gold complexes and nanoparticles to create invisible gold. Decreasing As in the fluid increased its partition into pyrite, resulting in arsenian pyrite precipitation with higher As contents enhancing surface adsorption and promoting gold nanoparticle formation within the pyrite lattice. The gold-quartz association is attributed to the piezoelectric effect of quartz during ore formation. The formation of visible gold in fractures within sulfide grains was controlled by the semiconductor properties of arsenopyrite and pyrite. Negative pyrite δ34S ratios at Huangjindong likely reflect a combination of fluid-rock interaction with the low-δ34S Lengjiaxi Group slate. Differences in pyrite δ34S ratios among mineralization styles at Huangjindong are mainly controlled by kinetic fractionation during rapid nucleation related to phase separation, as well as local redox variation and lithological heterogeneity.