Sorry for overlooking this post - I'll move it out of ID Required and edit the title to attract the attention of the Spanish Colonial experts we have.
Before we begin, it should be noted that the vast majority of Spanish colonial silver coins from the 1600s are very crudely struck "cob" coins, which are irregularly shaped and usually have much of their design missing. This coin, being round and with all of its design clearly visible, isn't your typical cob coin; it's purporting to be a presentation or "royal" coin, which is much scarcer and more valuable. If genuine, it would be worth thousands, even with the hole in it.
I would, therefore, start from the assumption that it is a replica, and try to disprove that.
First off, the hole itself makes me suspicious. These coins are suposed to be thick and heavy; the place where the hole is punched through looks rather thin.
Second, the appearance. It has the look of a coin that has been given a silver "wash" which has degraded over time. Now, that could just be strange toning, picked up from sitting in collections for several centuries. But it makes me suspicious.
The clicher will be the weight. If it's the thin base-metal replica that I suspect it might be, then it won't weigh anywhere near the 27 grams it is supposed to weigh.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis