The phrase "mask of a" is correct and usable in written English.
For example, you can use it to describe a particular type of mask, such as "He wore a golden mask of a lion on his forehead."
Everyday Isis makes Islam wear the mask of a barbarous sexual monster".
His face is the blank mask of a man for whom duty is life.
"They are going to wear one mask, and that's the mask of a union buster".
He portrayed Walpole as a strange genius, and gave Sterne an almost demonic mask of a face.
Meanwhile, my husband was coveting a mask of a rat eating a man's head ($24.98 at Costumesandmasks.com).com
Boldin's chin dropped, his helmet lifted and his momentum drove him into the face mask of a charging Smith.
Her wide eyes staring hawklike out of her angular mask of a face, Ms. McElhone's Rheya projects a forbidding sensuality.
I saw one man wearing a mask of a pig's head, and another dressed as a skeleton.
At one point, the camera shoots a scene through the latticed face mask of a burka hood.
