Geological Sampling and Magnetic Surveys of a Tungsten Occurrence, Bonanza Creek Area, Hodzana Highlands, Alaska.
The tungsten occurrence at the margin of the Kanuti Batholith in the Bonanza Creek area was investigated by the Bureau of Mines for the Bureau of Land Management as part of an inventory of mineral deposits within and bordering the trans-Alaska oil pipeline corridor. Fieldwork was conducted over a period of 6 weeks during the summer of 1979. Analyses and sample location maps were compiled from stream sediment, panned concentrate, soil, and rock samples. Analytical methods included atomic absorption, x-ray fluorescence, emission spectrography, and neutron activation. Tungsten and molybdenum, in the minerals scheelite and molybdenite, were found in trace amounts throughout the 30-mi2 project area. The highest grade tungsten mineralization was found in a pyrrhotite-rich chalcopyrite- bearing tactite. The tactite occurs in pods up to 10 ft wide. Scheelite was most commonly found in a relatively sulfide-free calc- silicate schist that was of lower grade than the tactite. Traces of molybdenite occur in quartz veins, pegmatite, and aplite dikes. Magnetic surveys show calc-silicate country rock to be more magnetically susceptible than granitic rocks. One magnetic anomaly of 1,700 gammas within calc-silicate schist coincided with a group of anomalous soil samples high in w, mo, pb, cu, and zn.