Putting everything else aside, what makes you think it's different. Is the weight different? Is its density different? Is its electrical conductivity different? Just because the color is different doesn't mean it's a different metal. A mix of oxidation, cleaning, and general Circulation marks is what I see.
In one of your posts, you say something like "over and under weight", the very first step would be to weigh these accurately. Before spending big bucks on certification, have a dealer look at them and give you an opinion. You aren't a new poster, and you have the best wishes of people here, even though you might not have their confidences.
All you need to do is find a gold buyer with an XRF analyzer; all the major ones and most of the minor ones do these days. They will be able to tell you the alloy composition on the spot.
The Op is never going to have the coins tested by anyone. He is just playing games with the folks here.
My bet is uranium and highly radioactive sent down in an unmarked spacecraft by alien collectors that grew up in China.
OK, time for silly season...perhaps it is the world's densest, most inert metal...administratium...look it up