I referenced having found a grain of platinum while panning gold in north Georgia, 30+ years ago, in the "greater" Dahlonega area.
To explain a little further and to give some insight as to how I determined that the grain was most likely platinum, I did a few tests on it (it was l - 1.5 mm in diameter, large enough to study). From the way it "behaved" in the gold pan, I determined that it had a slightly-higher specific gravity than gold (check). It was maleable (check), it was light gray to whitish gray (check) and it was lightly magnetic - see below (check). Worked for me.
Though I don't remember where, I seem to remember that some element that commonly is in a natural alloy with platinum is magnetic. This Wikipedia entry is interesting, though it doesn't mention the magnetism property. Perhaps a tiny bit of nickel and/or cobalt? As one would expect platinum from mafic rocks, nickel would also likely be present in at least trace quantities.
Being a coin-collector at the time, I took the flattened grain and stapled it into a cellophane-center cardboard holder, which has been misplaced during one of the times that we moved. I am not convinced that it is gone forever. There are still a few boxes unopened from the last couple of times that we moved. Such as it is when we get older.