Magnetite deposits at Tuxedni Bay, Alaska

The magnetite deposits on an island in Tuxedni Bay occur in contact-metamorphosed volcanic and sedimentary rocks near their contact with a quartz diorite batholith which underlies large areas of the adjacent Aleutian Range. The deposits are pyrometasomatic in origin and are localized along northeast-trending fractures. The eastern deposit is a low-grade disseminated deposit occurring in hornfels. The western deposit occurs as a massive lens of magnetite and garnet with a marble hanging wall and a hornfels footwall. The tenor of mineral rock in the western deposit may average 75 percent of magnetite. The deposit is lenticular and can be followed along strike for 55 feet in outcrop and, where concealed beneath a cover of soil and vegetation, can be followed for an additional 55 feet with a dip needle. Where exposed in a sea cliff the deposit is 30 to 35 feet thick.