Contribution of bismuth melts to gold endowment in the Baolun gold deposit, Hainan Island, South China
Year: 2024
Type: article
Abstract: • Primary evidence of Au-Bi melts was preserved in Baolun hydrothermal Au deposit. • Mesothermal, low- f S 2 and reduced hydrothermal conditions was verified for Baolun. • The Au-Bi hydrothermal system at Baolun fits with the Au–Bi binary phase evolution. Bismuth (Bi) melts and related polymetallic alloys can efficiently scavenge gold (Au) from Au-unsaturated aqueous solutions, contributing to the Au endowment in many hydrothermal deposits. However, original evidence for Au–Bi melts is often poorly preserved due to post-precipitation alteration. This complicates investigation of the liquid bismuth collector model in hydrothermal Au deposits. Here we present primary evidence for the occurrence of Au–Bi melt in hydrothermal systems through an examination of the Au–Bi phases and textures in the Baolun Au deposit (Hainan Island). This study found that maldonite, native bismuth, Au–Bi symplectite and Au–Bi melt blebs appeared successively following the precipitation of native gold. Notably, large Au–Bi melt blebs were well preserved in natural systems due to the rapid cooling of fluids. The mineral assemblages and their corresponding fluid physiochemical conditions suggest that the evolution of the ore fluids at Baolun was characterized by a continuous reduction in Au and Bi concentrations and Au/Bi ratios alongside decreasing fluid temperatures and sulfur fugacity ( f S 2 ). These observations offer direct evidence for Au scavenging by Bi melts in a mesothermal (275–450 °C), low- f S 2 and reduced hydrothermal system, aligning well with the Au–Bi binary phase evolution established in metallurgy. As the fluid cooled further, the Au–Bi phases were subsequently overprinted by later Te–S-rich fluids, as evidenced by the formation of bismuthinite, jonassonite, and joséite-A around the Au–Bi phases. Importantly, our study reveals that the Baolun Au deposit is characterized by a Au–Bi–Te hydrothermal system and that the metamorphic country rocks at Baolun are the major source of Au, Bi, and Te.
Source: Ore Geology Reviews
Authors: Shuang Yan, Qiang Shan, Deru Xu, Xueyuan Yu
Language: English
Subfield: Economics and Econometrics
Domain: Social Sciences
Open Access status: gold
Estimated APC paid: $2,620
OpenAlex ID: W4402788379