Public-data File 89- 17 GEOLOGY AND MINERAL RESOURCES OF THE RUSSIAN MISSION C-1 QUADRANGLE, SOUTHWEST ALASKA T.K. Bundtzen and G.M. Laird Alaska Division of Geological and Geophysical Surveys January 1990 THIS REPORT HAS NOT BEEN REVIEWED FOR TECHNICAL CONTENT (EXCEPT AS NOTED IN TEXT) OR FOR CONFORMITY TO THE EDITORIAL STANDARDS OF DGGS. 3700 Airport Way Fairbanks, Alaska 99709 CONTENTS Page Abstract ......................................................................................................................................................................... Introduction and geography ....................................................................................................................................... Acknowledgments....................................................................................................................................................... Geologic units .............................................................................................................................................................. Introduction ............................................................................................................................................................. Gemuk group ........................................................................................................................................................... Kuskokwim group ................................................................................................................................................... Volcanic-plutonic complexes ................................................................................................................................. Volcanic rocks ..................................................................................................................................................... Plutonic rocks ...................................................................................................................................................... Dikes and sills .................................................................................................................................................... Petrogenesis and age of volcanic-plutonic complexes. dikes and sills ......................................................... Hornfels .................................................................................................................................................................... Pliocene-Early Quaternary basalt ......................................................................................................................... Quaternary deposits .............................................................................................................................................. Deposits of glacial origin .................................................................................................................................. Colluvial dominated deposits ............................................................................................................................ Fluvial deposits ............................. ................................................................................................................. Structure ....................................................................................................................................................................... Economic geology ........................................................................................................................................................ Introduction ........................................................................................................................................................... Lode deposits ........................................................................................................................................................... Owhat prospect ................................................................................................................................................... Louise prospect .................................................................................................................................................. Headwall prospect ............................................................................................................................................. Mission Creek or 'Konechney' prospect ........................................................................................................ Other lode prospects in the Russian Mountains ............................................................................................ Lode deposit paragenesis .................................................................................................................................. Placer deposits ......................................................................................................................................................... Industrial minerals and fuel ................................................................................................................................... Aggregate ......................................................................................................................... Riprap .................................................................................................................................................................. Bibliography ............................................................................................................................................................... TABLES Table 1. K-Ar analyses of selected rock samples from Russian Mission C-1 Quadrangle. Alaska ............... 25 2. Major oxide analyses and CIPW norms of igneous rocks from Russian Mission C-1 Quadrangle. Alaska ................................................................................................................................ 26 3. Analytical results from prospects and mineral occurrences in the Russian Mission C-1 Quadrangle, Alaska ................................................................................................................................ 27 FIGURES Figure 1. Location map showing Russian Mountains and adjacent lowland ...................................................... 2 2. Fence diagram of Late Cretaceous volcanic section (on plate 1) ................................................... Pocket 3 . Plot of Russian Mountains volcanics on K20-Si02 compositional diagram after McBirney (1984) ..................................................................................................................................... 7 4 . Rare-earth element variation diagram showing three basaltic andesite samples from Russian Mountains, Alaska .................................................................................................................................. 7 5. Rare earth element variation diagram- of intrusive rocks from Russian Mission, Alaska ......................................................................................................................................................8 6. Quartz-K-spar-plagioclase plutonic classification scheme for Cretaceous granitic rocks from Russian Mission C-1Quadrangle .........................................................................................................10 7. Normative orthoclase-albite-anorthiteplot of plutonic rocks, Russian Mission C-1 Quadrangle .............................................................................................................................................11 8. AFM plot of plutonic rocks from Russian Mission C-1 Quadrangle, Alaska .................................... 12 9. Peacock diagram plot of volcanic and plutonic rocks from Russian Mission C-1 Quadrangle, Alaska .......................................................................................................................................................13 10. Map showing extent of Quaternary glacial advances in the Russian Mountains massif, modified from Kline and Bundtzen (1986) ............................................................................ 14 11. Grain size distribution of Mission Creek, Fan, Russian Mission C-1 Quadrangle, Alaska ............. 22 PLATES Plate 1. Geologic map of the Russian Mission C-1 Quadrangle, Alaska .....................................................Pocket 2. Mine maps of gold-arsenic-copper prospects in the Russian Mountains, Russian Mission C-1 Quadrangle, Alaska .....................................................................................................................Pocket iii GEOLOGY AND MINERAL RESOURCES OF THE RUSSIAN MISSION C-1 QUADRANGLE, SOUTHWEST ALASKA T.K. Bundtzen and G.M. Laird ABSTRACT The Russian Mission C-1 Quadrangle is a 522 km2 (204 mi2) area near the western edge of the Kuskokwim Mountains, an upland dominated by accordant rounded ridges, isolated glaciated massifs, and broad sediment filled lowlands in southwest Alaska. The study area is sparsely populated with Chauthbaluk (population 185) being the only community with year-round residence. The Kuskokwim River passes through the area from east to west and bifurcates the area into uplands (north) and lowlands (south). The region is dominated by the glacially carved Russian Mountains, which protrude above lower rounded hills to elevations of 1,059 m (3,466