Near term multi bagger and tin producer, page-353

I don't think they would make a mistake, particularly with BDO auditing it too. Also, I'm just trying to suss it out rather as to satisfy my curiosity.

The costs are written confusingly.
Is the opening inventory, $530,000, their costs? What they paid for it? If yes, how come it's in their 2016 costs too? Is it the as for 2016/17 FY? Also, it should be placed in brackets as negative.
The closing inventory would then make sense as a total of 2017 expenses on their production + price of opening inventory. Calculating their costs per ton, it makes about 58t of the concentrate.

MB