It's not quite stargate. The effect with a single card is David Britland's Trapdoor Card, which is a handling for Bob Neale's Trapdoor (which was done with a file card).
Stargate is two Trapdoor cards stuck together.
Bob's original is in Lifesavers, Britland's version was in the Magic Menu 1-5, Stargate is a commercial effect.
Hope that clears things up
Ian