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). This map shows the distribution and abundance of copper in stream-sediment samples.
Stream-sediment samples were collected at 569 sites 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.
The 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 copper and 15 other elements by a semiquantitative spectrographic method (Grimes and Marranzino, 1968). Other splits were analyzed for gold and zinc by atomic absorption methods (Warren and others, 1969).
Sample sites and copper values (in parts per million) are indicated on the map by symbols identified in the histogram. The weakly anomalous values are considered to be significant only where they were detected in stream-sediment or heavy-mineral concentrate samples that also contained strongly anomalous values of other metals such as arsenic, gold, lead or tungsten.
The map shows two populations for copper in stream sediments. One population consisting of generally lower copper values represents the samples collected from the sedimentary terrane in the central and western parts of the quadrangles. The other population consisting of generally higher copper values includes samples collected in areas of sheeted basalt dikes and pillow basalts in the eastern part of the quadrangles and from the sedimentary terrane of Latouche Island; in these areas chalcopyrite and pyrite were observed as fine-grained disseminations in the rocks and as mineral particles in the heavy-mineral concentrates.
