Call me crazy... I tried the magnet trick on my own packs I already bought, in curiosity, and got 3 for 3 Silver border packs and obviously magnet too but only 1 for 1 on that so far.
To repeat, I was not pack searching in the strictest of terms because I was searching my own already bought packs. It is very slightly magnetic with the silver packs. I would almost assume gold would too but haven't been that lucky yet and having only opened 12 packs, obviously haven't came across gold. Also I realize "gold" isn't magnetic but neither is "silver" so...
(btw, a really strong magnet, NdFeB about 1/2 inch long 1/4 inch diameter rod type)