From abstract: Gypsum-bearing rocks crop out in Gypsum and Yellow Jacket Gulches, on Sheep Mountain, which is about 90 miles northeast of Anchorage, Alaska. The gypsiferous rock occurs in deposits of irregular shape in the greenstone. Both the gypsiferous rock and the greenstone are hydrothermal alteration products of the volcanic rocks of Jurassic age which comprise the bulk of the mountain. Near-surface samples of the gypsiferous rock contained an average of 25 to 30 percent gypsum ; some contained as much as 50 percent. Quartz, alunite, clay, sericite, and pyrite are contaminating constituents of the ore. Six of the largest and most accessible of the gypsum deposits were mapped and calculations show that three of the deposits contain an aggregate of approximately 311,000 short tons of indicated gypsiferous rock and four of the deposits contain 348,000 short tons of inferred gypsiferous rock.