If they're not in a rush to process the sulphides, they've got...

If they're not in a rush to process the sulphides, they've got ~5 years or so to figure out the leeching before they need to make a decision on using it, giving a year or so buffer before the oxides run out. Selling the concentrator for now seems like a reasonable move instead of letting it sit there and having to spend the upkeep for care and maintenance and the physical space it takes up. Even if the concentrator is the way to go in the end, it'd likely still require refurbishment which also wouldn't be cheap. Sell now for some cash, in 5 or so years time there should be enough cash printed to afford a new concentrator if needed.