why should a bank charge gst on old gold auctioned by them

Auctions Gold (26 Points)

18 July 2017  
if an individual places as collateral old gold jewellery to a bank and takes a gold loan. he defaults ...so does not pay back the loan. the bank then auctions that gold. bank is not a trader...as they are not allowed to do business of old gold sales...when they sell the old gold jewellery to a refiner of gold or to a jeweller/trader.. will there be gst applicable at this stage by the bank to the refiner or to the trader?