This appears as quite a scary mask when you first approach it – perhaps its original purpose!
It is from Northern New Ireland which I had not heard of until I visited Sainsbury Centre to see the mask. I have now learned that it is close to (if not part of) Papua New Guinea.
The Sainsbury Centre catalogue notes that the mask “is both sculpturally exceptional and unique in form” noting that “similar masks have not been found in the literature”.
My notes are here Mask