The gold colored flakes are most likely shavings from a bushing in the trans. The silver chunks could be just about anything, but no mater what they are, it is serious. I would not try to drive the car anywhere other than directly to your favorite tranny shop.
Keep in mind that a GM dealer can install a GM Goodwrench rebuilt trans that comes with a 3 year, 100,000 mile nation wide warranty for around $3,000 depending on where you live. That warranty is hard to match let alone beat when it comes to transmissions. And the price isn't that much higher (sometimes even lower) than a trans shop that will only give you 1 year, 12,000 mile warranty.
LOL, can you tell who I work for?