Within the Birimian and Tarkwaian lithologies of Ghana there are three major types of gold mineralisation:
Type 1: Reef, Vein or Lode gold deposits associated with regional scaled shear zones, such as the Obuasi gold mine to the north of Kubi.
Type 2: Granitoid-hosted, mesothermal gold mineralisation, such as Ayanfuri gold mine to the south west of Kubi.
Type 3: Auriferous quartz-pebble conglomerate deposits such as at Tarkwa and recent alluvial gold concentrations.
The Kubi deposit mineralisation style is Type 1: Birimian aged, shear hosted, reef, vein or lode gold deposit.
Mineralisation
The mineralisation occurs in a 1.0 to 15.0 metre thick garnetiferous horizon within Birimian metasediments. This garnetiferous horizon contains fine grained gold associated with minor (5-15%) pyrite, arsenopyrite and pyrrhotite as well as some coarser gold which is associated with relatively narrow quartz veins. Some mineralisation occurs in quartz veins and veinlets that cross-cut the Birimian-Tarkwaian contact, outside of the main garnetiferous horizon.
SEM (scanning electron microscope) and polished section studies have observed gold and associated sulphides such as pyrrhotite, pyrite, arsenopyrite and occasionally chalcopyrite, rimming and often replacing the included garnet blasts. The garnets are often highly tectonised with native gold, often coarse, and with sulphides coating the micro-fractures.
The grades exhibit ........
