A FIELD EMISSION SCANNING ELECTRON MICROSCOPY (FESEM) INVESTIGATION OF THE TEXTURE AND MINERALOGY OF MACROCRYSTALLINE GOLD FROM TYPE 4 ORE FROM ROUND MOUNTAIN, NEVADA
Previous microscopy studies on gold from Round Mountain may have used samples that had been rinsed in acids which would have likely removed paragenesis minerals. Textural analysis as well as compositional analysis using energy dispersive spectroscopy (EDS) was conducted in order to identify paragenetic minerals on the unmodified crystals. Paragenetic minerals identified are dominantly smectite and apatite. These minerals were found in depressions and apparent dissolution pockets across the entire surface of the gold. Various microtextures were present on the surface of the gold crystals. Gold textures included hopper steps and euhedral “ghost” crystals, regions where an unidentified crystal had dissolved. Smectite is primarily found as typical cornflake lamellae aggregates. Apatite was euhedral and tabular with irregular crystal faces. Data suggests that there was possible dissolution of primary gold and perhaps other intergrowth minerals, followed by secondary growth of the paragenesis minerals on the crystals. Fungal hyphae were found on the surface of the gold in association with the paragenesis minerals. The relationship between the gold and fungus is not yet fully understood. FESEM investigation indicates that mineralization history is more complex and shows distinct paragenesis sequence for macrocrystalline gold at Round Mountain.