I don't know much about Haudenosaunee ceremonial masks. I do know they can be incredibly powerful, and that they play a vital role in the culture and spirituality of Six Nations People. You might find out it is made of White Pine, but does it really matter? What would matter to me is having it returned to the People. An artifact such as this, purchased at an auction, carries with it a history of exploitation, abuse and possibly more. It's beyond me why anyone would want to retain such a piece in this day and age when we are much more aware of issues of grave-robbing, appropriation, and exploitation. Why anyone would want a "souvenir" commemorating such deceit and abuse is beyond me.
If he doesn't know anything about it, have him return it to those who do. The fact that both you and "the gentleman" want to protect the artifact tends to make me believe that you are both aware of the inappropriateness of it being in your possession. That you are both guarding it reveals that you know it is a lot more important and valuable to others than it is to you. At some level I think you are both aware of the strong medicine that is a part of this mask.
Do you live in eastern Canada/US? If it were me, I would begin by making contact with Haudenosaunee Confederacy leaders. The "gentleman" should be made aware that having this mask in his possession is not only inappropriate and exploitive but quite probably illegal. Every effort should be made to return it.
Edited to add: My friend spoke with her Mohawk husband who says it could be taken to a museum to be repatriated back to the People. Unless the "gentleman", and you too, know how to care for this mask, he says "you should not be fooling around with it." It is likely made of cherry wood. Because neither of you know where it came from, or what it was used for, he says it is "nothing to fool with" and could cause problems, if it hasn't already, for you both.
