USGS1978
Reconnaissance geochemical and mineralogical sampling was done in the Talkeetna Quadrangle during 1975 and 1976 as part of the Alaska Mineral Resource Assessment Program (AMRAP). These maps show the distribution of gold, scheelite, chalcopyrite, arsenopyrite, galena, fluorite, cinnabar, and malachite in the nonmagnetic fraction of heavy-mineral concentrates. Heavy-mineral concentrate samples were collected at 812 sites from active stream channels. The heavy-mineral concentrates were obtained by panning stream sediment in the field to remove most of the light minerals. The panned samples were then sieved through a 20-mesh (0.8 mm) sieve in the laboratory, and the minus-20-mesh fraction was further separated with bromoform (specific gravity, 2.86) to remove any remaining light-mineral grains. Magnetite and other strongly magnetic heavy minerals were removed from the heavy-mineral fraction by use of a hand magnet. The remaining sample was passed through a Frantz Isodynamic Separator and a nonmagnetic fraction was examined for its mineralogical content with the aid of a binocular microscope and an x-ray diffractometer. The nonmagnetic concentrates primarily contain phyllite fragments, muscovite, sphene, zircon, apatite, tourmaline, rutile, and anatase. Most ore and ore-related minerals also occur in this fraction.