In Explorers its Chief Scout Diamond, then Platinum before Queens Scout Award. The 3 levels pretty well match the 3 Duke of Edinburgh Award levels. (I'm an Explorer Scout Leader as well as a modeller. When we camped last weekend I was woken by a 57/6 and then a few hours later a 60!)
I think you get your platinum first because I've just achieved that too, but messed up the date of the presentation, so technically haven't got it yet....
I didn't do anything for it, you're right, I got it for doing my DofE bronze expedition.