From ore to concentrate -a systematic geometallurgical study on the Cavanacaw Au Deposit, Northern Ireland

A systematic geometallurgical assessment was carried out to follow changes of mineralogical composition and microfabric following the ore extracted from a single mined block extracted at the Cavanacaw Au Mine from the open pit (in situ ore) through the entire beneficiation process. SEM-based image analyses was used as major analytical tool to carry out the investigation on the finely disseminated Au ores. First of all no Au was found in the tailings, the beneficiation plant recovers the bulk of the sulfides and electrum to the concentrate, and finally Au liberation is good. Despite of these positive assesment results illustrate, there are still some losses that appear to be systemic. In particular, large electrum grains (>60 µm) that are abundant in the original uncrushed material only make a minor contribution to the final concentrate. Due to the ductile behaviour of electrum, fracturing of larger electrum grains into smaller grain sizes appears unlikely – it is thus suspected that these larger particles may be lost during processing.
Furthermore, our results clearly reveal that narrow high grade and sulphide-rich veins are higher in gold grade than the final flotation concentrate. This results from processing a mixture of high grade ore and partly mineralised wall rock. To reduce processing costs it should thus be considered to introduce optical sorting to separate the high-grade vein from lower grade mineralised wall rock. Such pre-selection may further improve recovery