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A nickel-bearing sill, about 126 feet thick, lies in a thick sequence of greenstone schists, graphitic phyllites, and quartzites near the north end of Admiralty Island not far from Juneau, Alaska. Petrographic measurements show that volumetrically the rock is made up of about 62.07 percent labradprite, 34.22 percent olivine, 2.42 percent pyroxene, 0.79 percent pyrrhotite, 0.21 percent magnetite, 0.14 percent chalcopyrite, and 0.06 percent pentlandite. By weight the rock contains about 0.20 percent chalopyrite and 0.10 percent pentlandite. The copper content in chalcopyrite therefore is about 0.067 percent and the nickel content in pentlandite about 0.025 percent. Chemical analyses of representative samples show the rock as a whole to contain about 0.350 percent copper and 0.344 percent nickel. The differences between the petrographic and the chemical results are believed to be due only in part to the fact that the few thin and polished sections studied may not be representative of the rock. The large differences appear to indicate that much of the nickel is present in the rock in some other mineral than pentlandite, presumably in olivine. LOCATION AND GENERAL FEATURES Several nickel-bearing deposits are known in southeastern Alaska, 1 although no significant quantities of nickel have been produced from Alaskan ores. The deposits have many features in common and are similar to many nickel-bearing deposits throughout the world. This paper deals with a nickel-bearing sill known at the outcrop as the "Mertie lode," near the north end of Admiralty Island (fig. 11) not far from Juneau. The country rocks of the vicinity comprise a thick sequence of greenstone schists, graphitic phyllites, and quartzites and several bodies of diorite or gabbro. The principal structural feature of the area is a large anticline that pitches about 30° SE. The nickelbearing sill lies high on the anticline but somewhat to the east of its apparent axis. Outcrops near the sill are poor, and the only natural i Overbeck, E. M., Geology and mineral resources of the west coast of Chichagof Island: U. S. Qeol. Survey Bull. 692, pp. 125-133,1919. Kerr, P. F., A magmatic sulphide ore from Chichagof Island, Alaska: Econ. Geology, vol. 19, pp. 369-376, 1924. Buddington, A. F., Alaskan nickel minerals: Econ. Geology, vol. 19, pp. 621-541, 1924; Mineral investigations in southeastern Alaska: TJ. S. Geol. Survey Bull. 773, pp. 95-113,1925; Mineral investigations in southeastern Alaska: U. S. Geol. Survey Bull. 783, p. 46,1926. Buddington, A. F., and Chapin, Theodore, Geology and mineral deposits of southeastern Alaska: TJ. 8, Geol. Survey Bull. 800, pp. 348-351,1929. 59013 39 263 264 MINERAL RESOURCES OF ALASKA, 1936 exposures are an outcrop along a small stream and another very small outcrop about 40 feet east of the stream. The deposit has been prospected by a tunnel 110 feet long and by several diamond-drill holes. At the outcrop along the stream the hanging wall is light-colored siliceous schist, about 20 feet thick, overlain by graphitic phyllite. The footwall is greenstone schist. The sill is about 126 feet thick, strikes N. 15° W., and dips 38° E. The rock is very dark, almost black, coarse grained, and contains I prospect described

Nickel content of an Alaskan basic rock