A new mechanism of formation of the silver-rim structure on primary gold grains

Abstract

Gold minerals in the Baochun skarn-type gold deposit are Au-Ag alloys with Ag contents within the range of 15–35. 5 wt% and the minerals vary from 5μm to 50μm in size. As viewed from the electron microprobe images, most gold grains show silver rims with a high Ag content as compared with the core, ranging generally from 2 to 3μm in width. From dynamic calculations based on the mass action and mass balance constraints on the crystallization of native gold, it is considered that the enrichment of silver in the rim of gold minerals is due to gradual enrichment of silver in the ore-forming solutions with its evolution from the early to the late metallogenic stage.