[Rich]

The color of the rust (reddish brown - assuming the photo is true
color) would make me think Shinshinto Period approx 1780-1870 ballpark
date. Nice tanto, take good care of it.

BTW, Jason is likely correct in that the mounts are possibly a mixed,
remounted set. This was not uncommon during Shinshinto period.
There were two periods of major production of tanto; the Koto (pre 1600)
and the Shinshinto. Shinshinto was a sort of "revivalist" period for the
Japanese sword. Not uncommon for smiths to "reuse" older mounts with
new blades they made. IMHO it doesn't detract from the tanto, just part
of its history.

Rich