Geologic description
The Lucky 7 occurrence is hosted by the Fish Lake mafic-ultramafic complex, which is considered to be a lopolithic feeder to the basalt flows of the Upper Triassic Nikolai Greenstone (Nokleberg and others, 1991). The occurrence consists of disseminated sulfides in a melagabbro in the lower part of the gabbroic unit of the second magmatic cycle of the Fish Lake complex (W.T. Ellis, unpublished data, 1996). The gabbroic package at the site includes leucocratic taxitic gabbro, troctolite, two-pyroxene gabbro, gabbronorite, and olivine melagabbro. The sulfides are disseminated in a 5-foot-thick melagabbro layer. The layer strikes about southeast and dips 45 degrees south. Sulfides, chiefly pyrrhotite and trace amounts of chalcopyrite and pentlandite, form 3 to 7 percent of the rock. Samples contain as much as 0.14 percent copper, 0.17 percent nickel, 94 parts per billion (ppb) palladium, and 94 ppb platinum (W.T. Ellis, unpublished field data, 1996). |
