Element Bonding Questioonnn?

First of all they are metallic bonding because they are both metals. The way the bond is under high pressure or heat and the metals fuse in one of two ways. Interstitial or substitutional. In the gold case it is substitutional. Atoms begin to replace each other ie. gold replaces some platinum and vice versa, and an alloy is created. Like all metals they share a sea of delocalised electrons