It looks like a preform or blank. Probably they didn't like the way it was chipping. You can find a ton of those in village and camp sites. Many times the Indians would take large and small stones...they would pre-work the small ones and knock blanks or preforms off the larger core stones. Then they could transport this smaller "blanked out" stones to other locations where they could be transformed into a completed arrowheads. If you ever run across one of these working areas you will readily recognize it because of the amount of flakes and chunks of chipped stone. On the down side, I once found an island in a lake that was absolutely covered with chips...could pick up literally 5 gallon buckets full of them.....found 2 points on the whole thing......guess they took it all with them and made few mistakes.
I would propose that this could be a hand-axe, in which case it is VERY old - similar hand-axes are online, if I were you I would do some more research on your very interesting find!
Oroblanco