Reduced copper-gold porphyry deposits26 Jan 2021 16:24
I found this comment interesting in yesterday's rns:
"The close association of pyrrhotite with the chalcopyrite copper mineralisation, suggest the Racecourse Mineral Resource is a reduced copper-gold porphyry deposit, in contrast to the oxidised porphyry copper-gold deposits, which are more common throughout the Lachlan Fold Belt in New South Wales. Reduced copper-gold porphyry deposits are known to have a higher proportion of gold in comparison to copper."
A bit of Googling of reduced copper-gold porphyries brings up an academic paper with the following title "Reduced porphyry copper-gold deposits: A new variation on an old theme" and the following abstract:
"It is a widely accepted fact that porphyry Cu-Au deposits form from highly oxidized ore fluids. Despite this assertion, several otherwise typical porphyry Cu-Au deposits exhibit clear evidence of having formed from relatively reduced ore fluids. These “reduced” porphyry Cu-Au deposits lack primary hematite, magnetite, and sulfate minerals (i.e., anhydrite), but contain abundant hypogene pyrrhotite, commonly have carbonic-rich ore fluids with substantial CH4, and are associated with ilmenite-bearing, reduced I-type granitoids. Based on a synthesis of theoretical, experimental, and
field data, a variation on the classic porphyry Cu model is proposed to explain the formation of reduced porphyry Cu-Au deposits and their relatively Cu-poor but Au-rich nature. The proposed reduced porphyry Cu-Au model does not contradict the current understanding of porphyry Cu-Au formation. Rather, it adds yet another variation on the theme of porphyry Cu-Au genesis."
Note this comment: "reduced porphyry Cu-Au deposits and their relatively Cu-poor but Au-rich nature". Sounds like gold may be relatively more important than copper in this porphyry and we shouldn't get too hung up on copper grades. It also sounds like our gold grades might be better than Cadia and Boda. Assays will be interesting.