Is it permissible to trade gold in international markets by purchasing a quantity of it with a bank guarantee, then selling it and reclaiming the guarantee?

The transaction mentioned involves two prohibitions: dealing with usurious banks without necessity, which is forbidden due to cooperation in sin and aggression; and purchasing gold with a deferred price, which is unlawful because it constitutes usury of delay (riba al-nasia), as the sale must be hand-to-hand when the types differ.