With all due respect, how do you know that "It is pure silver and totally original and not a fake" when you came here not even knowing what it was? Were the other coins in the box ancient coins as well, with reliable collection/identification info? While the pictures are a bit blurry, the hole has rounded edges, consistent with a casting flaw and inconsistent with being poked by something sharp. In the strange lighting of your pictures the coin appears to be made of Pewter, but perhaps some better pictures and natural lighting would help the experts here provide a solid identification. Alexander tetradrachms are some of the most widely counterfeited coins in the world, ancient or otherwise (with better ones made from essentially pure silver, so that alone isn't proof of authenticity), so outside the context of reputable coin dealer inventory and wisely assembled collections random loose examples require some scrutiny.
It may well be authentic, but without better pics/info/weight it is one that I as an ancient coin collector would take a pass on.