GEOLOGY AND GEOCHEMISTRY OF THE CRAIG A-2 QUADRANGLE AND VICINITY, PRINCE OF WALES ISLAND, SOUTHEASTERN ALASKA BY Gordon Herreid, Thomas K. Bundtzen, and Donald L. Turner GEOLOGIC REPORT 48 STATE OF ALASKA Jay S. Hammond, Governor Robert E. LeResche, Commissioner, Dept. of Natural Resources Ross G. Schaff, State Geologist STAFF C.M. Adams. Cartographer L.F. Larson, Publications specialist M.R. Ashwell, Laboratory assistant W.E. Long, Hydrologist N.J. Bragg, Secretary W.M. Lyle, Petroleum geologist G.A. Broker, Clerk-typist R.A. Mann, Clerk M.E. Brown, Geologic information technician U.O. McBride. Clerk T.K. Bundtzen, Mining geologist D.L. McGee, Petroleum geologist C.N. Conwell, Mining engineer J. Newgaard, Accountant P. Coonrod, Clerk-typist G.H. Pessel, Petroleum geologist N.D. Coursey, Geochemical analyst R.D. Reger, Geologist C.L. Daniels, Geological assistant J.R. Riehle, Geological engineer J.T. Dillon, Mining geologist R.G. Schaff, State Geologist G.R. Eakins. Chief mining geologist L.C. Schell. Cartographer K.S. Emmel, Geological assistant R.H. Schultz, Laboratory technician W.G. Gilbert, Mining geologist D.R. Stein, Assayer S.W. Hackett. Exploration geophysicist C.H. Stevenson, Geologic information technician M.W. Henning, Mining geologist N.C. Veach, Assayer chemist J.T. Kline. Geological assistant G.M. Zartman, Clerk C.C. Landis. Clerk For sale by Alaska Division of Geological and Geophysical Surveys, P.O. Box 80007, College, 99708; 3327 Fairbanks St., Anchorage, 99503: P.O. Box 7438, Ketchikan, 99901: and Pouch M, Juneau, 99811. CONTENTS Page Summary ................................................................................................................................................................... Scope of present investigations .................................................................................................................................. Previous investigations ............................................................................................................................................... Geography ................................................................................................................................................................. Geologic units ............................................................................................................................................................ Wales Group.......................................................................................................................................................... Introduction ..................................................................................................................................................... Marble (Wm).................................................................................................................................................... Dolomite-rich marble ( Wdm) ............................................................................................................................ Dark-gray phyllite (Wp).................................................................................................................................... Phyllite, marble, and green schist (Wpmg)...................................................................................................... Green tuffaceous schist (Wg)............................................................................................................................ Metakeratophyre tuff(?) and related rocks (K, Kxt, Kd).................................................................................. Quartz sericite schist (Ws)................................................................................................................................ Silicified schist (Wss)........................................................................................................................................ Phyllite and limestone (Wpl)............................................................................................................................ Migmatitic gneiss (Wgm)................................................................................................................................... Age of the Wales Group.................................................................................................................................... Descon Formation ................................................................................................................................................ Introduction ..................................................................................................................................................... Spilite(?) and mixed volcanic rocks (Odv)........................................................................................................ Sheared conglomeratic graywacke (Odsg)......................................................................................................... Banded mudstone (Odm)................................................................................................................................. Graywacke (Odg)............................................................................................................................................. Argillite (Oda)................................................................................................................................................ Basalt (Odb)..................................................................................................................................................... Age of the Descon Formation .......................................................................................................................... Silurian(?) igneous rocks....................................................................................................................................... Altered granodiorite (Sgd)................................................................................................................................ Alaskite (Sa)..................................................................................................................................................... Keratophyre(?) (Sk)......................................................................................................................................... Devonian bedded rock units .................................................................................................................................. Introduction .................................................................................................................................................... Basal conglomerate and red beds (Dbc, Dar) .................................................................................................... Argillite-siltstone (Da), siltstone-graywacke (Dsg), pebble-conglomerate (Dpc), limestone (Dl), and felsite pebble conglomerate (Dkpc)............................................................................................................. Age ................................................................................................................................................................... Andesite(?) (Dand)............................................................................................................................................... Paleozoic(?) dikes (Pdk)........................................................................................................................................ Introduction..................................................................................................................................................... Felsite dikes ..................................................................................................................................................... Amygdaloidal porphyritic basaltic andesite dikes ............................................................................................. Porphyritic diabasesdikes .................................................................................................................................. Amygdaloidal porphyritic andesite dikes.......................................................................................................... Thermally metamorphosed dikes...................................................................................................................... Structure .......................................................................................................................................................... Age ................................................................................................................................................................... Cretaceous intrusive rocks ..................................................................................................................................... Altered porphyritic diorite (Kdip).................................................................................................................... Granodiorite (Kgdi)........................................................................................................................................ Epidotized gabbro and diorite (Keg).............................................................................................................. Breccia dikes (Kbd).........................................................................................................................................