Oiva gold-quartz dyke in the Lapland granulite belt, Laanila, Northern Finland
As an adequate sample processing technology, the liberation process by high voltage selective fragmentation system (selFrag) enables-3D investigation of gold/electrum grain surfaces with respect to structures, replacement and alteration. It provided an opportunity to extract additional information on the formation, deposition and distribution of gold, electrum and related minerals.
Mineralogical evidences imply two distinct but continuous stages of Ag-Au mineralization: primary hypogene and secondary either supergene or late stage, low-temperature hydrothermal. Primarily, Ag-Au as electrum and argentite (acanthite at present) might have deposited with chalcopyrite and other base metal sulfides. Textural evidence further supports late-stage remobilization of at least some of the gold and silver. Deposition/precipitation of fine grains (<20µm) of gold and electrum on the surface of goethite, Au composition variation core to outer surface of electrum grains, the presence of rim, wire and sponge morphologies in association with acanthite suggest remobilization of some Au and Ag during late-stage hydrothermal or supergene environment.
Gold/electrum grains (irregular, grooved and flaky) in the HM concentrate (monazite, zircon, Fe-Ti oxides, cpy) (OS-08-4.2).