It is quite rare for a CB to directly lease to a user, CBs usually lease to a bullion bank who then on lends it. In any case, a majority of these transactions are done via London, as it is an established central point for clearing trades. First, while the RBA has allocated, it would be converted to unallocated. A refinery receives physical from miners and after refining they usually either:
1. Sell it to the refinery for cash. In this case the refinery would sell the unallocated they leased in London to generate the cash.
2. Miner needs unallocated credited to their account in London (to settle financing transactions they have done, or forward sales etc) so refinery would transfer their London unallocated to the miner's account.
In both cases the refiner loses London unallocated but gets title to physical in their business. This effectively means they swap from unallocated in London to physical in their business.
When they sell whatever gold product they have made, they are immediately buying unallocated on the open market, so they know what the "cost" of the gold is/will be. Same with the hedging by futures example, they sell the product and immediately buy replacement gold.
