Reconnaissance geochemical and mineralogical sampling was done in the Seward and Blying Sound quadrangles during 1975 and 1976 as part of the Alaska Mineral Resources Assessment Program (AMRAP). These maps show the distribution and abundance of gold and silver in heavy-mineral concentrates. 

Stream-sediment and heavy-mineral concentrate samples were collected from active stream channels and locally, from the interface of streambeds with intermediate- to low-tide beaches. Most of the stream sediment is fine- to coarse-grained sand, with a clay-silt fraction in streams discharging from glaciers. Stream sediment samples were air dried and sieved through a 80-mesh (0.2 mm) sieve, and the minus-80 mesh fraction was saved for analysis. A split of each sample was analyzed for gold by a 10 gram atomic-absorption method (Ward and others, 1969). Another split was analyzed for 16 elements by a semiquantitative spectrographic method (Grimes and Marranzino, 1968).

The heavy-mineral concentrates were obtained by panning stream sediments in the field to remove most of the light minerals. The panned samples were sieved though a 20-mesh (0.8 mm) screen 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 Separator¹ and a nonmagnetic fraction was obtained at a setting of 0.6 amperes. A split of this fraction was pulverized and analyzed for 16 elements including gold and silver by semiquantitative spectrographic method used for analyzing the stream sediment. The remaining split of the nonmagnetic fraction was examined for its mineralogic composition using a binocular microscope and X-ray diffraction. The nonmagnetic concentrates primarily contain muscovite, sphene, zircon, apatite, rutile, and anatase. Ore minerals such as gold, scheelite, minium, and most sulfides are also found in this fraction.

Sample sites and gold and silver values (in parts per million) are indicated by symbols as defined in the histograms. The maps show two populations for gold in stream sediments and for gold and silver heavy mineral concentrates. One population consists of generally higher gold and silver values found in samples collected in the sedimentary terrane in the western half of the area. The other population consists of generally lower gold and silver values found in samples collected in areas of sheeted basalt dikes, pillow basalts, and sedimentary terrane in the eastern half of the area. The anomalous silver values found on Knight Island and Latouche Island are associated with chalcopyright- and pyrite-bearing rocks. 

¹ The use of trade names is for descriptive purposes only and does not constitute endorsement of those products by the U.S. Geological Survey.