Although the production costs have been recorded on the cashflow...

Although the production costs have been recorded on the cashflow statement for the past quarters, at best that is only a rough indicator especially when a mine is in start up phase. Without any proof of theoretical AISC I would advise that using a simple straight line deductive formula to  derive the sales figure is dangerous.  
However we do have the benefit of a lot of inventory that would have been categorised as production  expense in previous cash flow statements. The 6 Monthly P&L and Balance sheet would give the best indicator at this stage. Lets hope the inventory is high.