Reflected Light Microscopy of Industrial Minerals

Abstract

A short-pulsed high-voltage selective fragmentation test was performed on representative samplesfrom Oiva’s gold-quartz-dyke to liberate gold and related minerals using selFrag Lab machine. SelFrag wasable to release individual grains of gold, electrum and other minerals of interest preserving their originaltexture, shape, size and provided an opportunity for detailed study of their morphology, surfacial features,grain size and composition.The mineralogy of gold and electrum is studied by light and electron microscopes using various nonmagneticheavy mineral concentrate of the fragmented samples. Composition varies from about 27.15 to96.06 wt% Au and from 3.5 to 72.85 wt% Ag with Ag/Au = 0.04–2.68, and scarcely associated with Ag & Bitellurides and native Bi. Morphologically, gold/electrum grains are irregular, globular, branched, grooved,subrounded, flaky and commonly <75 μm in size.Based on mineralogical evidences, electrum might have been hydrothermally deposited and partiallyremobilized by supergene processes for the depletion of its silver to form fine-grained native gold. Suchsecondary enrichment might also be supported by the presence of acanthite, iodargyrite and covellite.