EVOLUTION OF INVISIBLE Au IN ARSENIAN PYRITE IN CARLIN-TYPE Au DEPOSITS

摘要

A significant characteristic distinguishing Carlin-type Au deposits from other Au deposits is the abundance of invisible Au in arsenian pyrite. Gold occurs primarily as ionic Au1+ in arsenian pyrite and is unstable during subsequent thermal events. In this study, we used the focused ion beam combined with scanning electron microscope (FIB-SEM) techniques, and a transmission electron microscope (TEM) to examine invisible Au and how it evolved through later geologic events that eventually led to the formation of Au nanoparticles. FIB-SEM techniques were used to prepare site-specific TEM foils from four Carlin-type gold deposits, including Getchell and Cortez Hills, Nevada, USA, and Shuiyindong and Jinfeng, Guizhou Province, China. These samples were analyzed to quantify ore pyrite chemistry and evaluate textures at the nanometer scale.