A tungsten-rich porphyry molybdenum occurrence at Bear Mountain, Northeast Alaska

Abstract

Molybdenum and tungsten porphyry mineralization occurs near Bear Mountain in northeast Alaska within a regional zone of small domes and intrusions. This zone can be traced 80 km to the west and easterly into Canada.A 50-ha (approximately 100 acres) mineralized area, defined by soil samples containing greater than 600 ppm Mo and 500 ppm W, is underlain by an altered complex of probable early Tertiary age consisting of rhyolite porphyry, quartz porphyry, intrusive breccia, and rhyolite porphyry dikes. The complex has intruded upper Paleozoic metasedimentary rocks.Surface exposures of rubble and limited outcrop are extensively leached; molybdenum occurs as molybdite oxides and tungsten occurs in both ferberite and huebnerite end members of the wolframite series. There is an apparent zonation from an upper tungsten-topaz zone capped by massive silica to a lower oxidized molybdenum-rich zone. A lead-rich halo surrounds the complex.