Mints are notorious for spreading everywhere. They will cross polinate and become a hybrid easily. It may be impossible to identify your mint. If you have a local master garden club or extension office they may come close. Many plants like oregano and marjoram are in the mint family. I grow my mint in large terra cotta pots. I don't let them out into the garden. They like to take over. I love my tea and adore my mint, but after a season or two, my peppermint is no longer the peppermint I had and my spearmint is a little off thanks to my bee yard. I find volunteers of mint everywhere. I consider them gifts. If you have mint anywhere it probably migrated easily. There are also wild mints like the appalachian mountain mint
