If there is some doubt in your mind about the correct accounting...

If there is some doubt in your mind about the correct accounting treatment for JV profit/(loss) I suggest you refer to Note 10 in ORE's FY2018 H1 Financial Statements. This shows quite clearly that it is the JV's after tax profit/(loss) (and after non-controlling interests) that is used to calculate the equity accounted profit/(loss) for inclusion in ORE's Profit/(Loss) account. Normal equity accounting treatment.
Hence changes in the Argentinian Tax Rate ("ATR") do have a measureable effect on ORE's PAT. The ATR is now 30% and will be reduced to 25% from 1/1/2020 so an additional benefit will accrue to ORE from there on in.