High Voltage Selective Fragmentation for Detailed Mineralogical and Analytical Information, Case Study: Oiva’s Gold-Quartz-Dyke in the Lapland Granulite Belt, Laanila, Northern Finland

Abstract

A short-pulsed high-voltage selective fragmentation test was performed on representative samples from Oiva’s gold-quartz-dyke to liberate gold and related minerals using selFrag Lab machine. SelFrag was able to release individual grains of gold, electrum and other minerals of interest preserving their original texture, 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 non-magnetic heavy mineral concentrate of the fragmented samples. Composition varies from about 27.15 to 96.06 wt% Au and from 3.5 to 72.85 wt% Ag with Ag/Au = 0.04–2.68, and scarcely associated with Ag & Bi tellurides 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 partially remobilized by supergene processes for the depletion of its silver to form fine-grained native gold. Such secondary enrichment might also be supported by the presence of acanthite, iodargyrite and covellite.