DEPARTMENT OF THE INTERIOR UNITED STATES GEOLOGICAL SURVEY GEOKGE OTIS SMITH, DIRECTOR BULLETIN 533 GEOLOGY OF THE NOME AND GRAND CENTRAL QUADRANGLES ALASKA BY FRED H. MOFFIT > $ CO WASHINGTON GOVERNMENT PRINTING OFFICE 1913 CONTENTS. Page. Preface, by Alfred H. Brooks___________________________ 7 Introduction_____________,_________________j______ 9 Field work __________________________________ 9 Published reports ______________________________ 10 Location and area of the district! _ _______________ 11 Typography ________ __ ______. 12 General features of Seward Peninsula_____ ___________ 12 Relief_____________________________________. 13 Drainage_____________ _ ________. 14 Descriptive geology __ _____ _________ 14 Outline of the geology of Seward Peninsula _______ 14 Stratigraphy of Nome and Grand Central quadrangles _______ 17 Kigluaik group _________ _______ 20 Lower formations___________ _ ___ 20 Tigaraha schist- _ __ _..__ 20 Age __ ___. 23 Intrusives associated with the Kigluaik group_______; ____ 23 Granite__________________________________ 23 Diorite_____________ _____________. 24 Diabase____________ ___ __________ 25 Pegmatite- 25 Age______ _____ - _______. 26 Nome group . __ 26 Schist____________ ___________ 27 Limestone__________ _ _________ 28 Age _ _ 31 Igneous rocks associated with the Nome group - ____ ______ 32 Greenstone __..__ 32 Granite-_____ _ __ __ . 33 Age___ _ .. _ 34 Veins_____________ _____________________ 34 Surficial deposits- 36 Unsorted waste _ _ _ 36 Stream gravel- 37 Elevated bench gravel . 38 Coastal-plain gravel 40 Silt_____________________-___-___________ 49 Glacial deposits- 51 Ice beds. 53 Structure _ 55 Historical geology .. 59 Economic geology 64 Introduction___ - -. 64 History of mining ____ 65 Economic conditions 68 3 4 CONTENTS. Economic geology Continued. Page. Mineral resources____________________________ _ 74 Metalliferous deposits_ _ ____________ _ __ 74 Placer deposits _______ _____________ ____ 74 Kinds of placers_____ _________________ 74 Residual placers _______________ ,.__ 75 Origin ___ ________ __ 75 Rock Creek__________________________ 75 Pioneer Gulch _____ __________________ 76 Boer Gulch_____ ________ 76 Nekula Gulch_____ ___________________ 76 Stream placers. _ 77 Principal classes __ ___ __ 77 Snake River basin _____________ 77 Snake River ____ __________________ 77 Anvil Creek_______________________ 79 Specimen and Nekula gulches________,____ 83 Glacier Creek- _______________^______ 84 Snow Gulch_______________________ 85 Hot Air bench ______________________ 85 Bonanza Gulch _ ______ __ 86 Rock Creek __________________________ 86 Lindblom Creek_____________________ 86 Balto Creek_________________________ 87 Boulder Creek ______________________ 87 Bangor Creek_______________________ 87 Last Chance Creek ___________________ 87 Goldbottorn Creek_____________________ 87 Steep Creek _______________________ 88 Grub Gulch__________________________ 88 Grouse Gulch __ ___________________ 88 Center Creek __________-_______________ 88 Cooper Gulch _______________________ 89 Bourbon Creek ____________ 89 Dry Creek and Newton Gulch________________ 90 Nome River basin__ __________________ 92 Nome River _ ____________ 92 Dexter Creek ______________________ 93 Grass Gulch _________________________ 94 Deer Gulch ________________________ 95 Left Fork_________________________ 95 Grouse Gulch___ _________________ 95 Buster and Lillian creeks_______________ 96 Osboru Creek_______________________ 97 Washington Gulch____________________ 98 Dorothy Creek______________________ 98 Extra Dry Creek_____________________ 98 Banner Creek__________ ..___________ 99 Basin Creek __ ________________ _ 99 Divide Creek _______________________ 100 Boer Creek ____________________ ___ 100 Streams not included in Nome and Snake River drainage. 100 Hastings Creek _______________________ 100 Fred Gulch ________________________ 101 Hazel Creek _______________________ 101 CONTENTS. 5 Economic geology Continued. Page- Mineral resources Continued. Placer deposits Continued. High bench placers- _ ____ _____ _ 101 Character and distribution.- _____ 101 Dexter station _________________________ 101 Specimen and Grass Gulch divide______________ 106 Dexter and Dry Creek divide_____________ 107 Summary___ _ ____________________ 108 Beach placers___________'________________ 109 General features_______________________ 109 Present beach________._________________ 110 Second beach __ _____________ ^ 111 Third beach __________________________ 112 Intermediate beach_____________________ 117 Submarine beach_______________________ 118 Monroeville beach_______________________ 119 Origin of the beach placers- 119 Gravel-plain placers______________________ 123 Dredging ________ __ _________ 124 Lode deposits ________ __ __ __ 126 General features.__________________________ 126 Gold___________ _ - -____________ 127 Bismuth_______________________________ 133 Antimony________ ______________ 133 Tungsten ______________ _________ 134 Copper _ ______ 134 Graphite_______________________________ 135 Index ___ 137 ILLUSTRATIONS. Page. PLATE I. Topographic map of Nome quadrangle___________ In pocket. II. Topographic map of Grand Central quadrangle_______ In pocket. III. Geologic map of Nome quadrangle______________ In pocket. IV. Geologic map of Grand Central quadrangle________ In pocket. N V. Geologic map of Seward Peninsula_________________ 14 - VI. A, View northward from Nome across the tundra; B, Glacial cirque 1 mile west of pass between Windy Creek and Cobble­ stone River______________________________ 14 VII. Geologic sketch map of region at heads of Grand Central River and Windy Creek__________________________ 20 VIII. A, Characteristic rugged ridge in the Kigluaik Mountains; B, Granite sills in the southward-dipping biotite schist of Thompson Creek____________________________ 24 I.. A, Summer remnants of an ice sheet that covered the flood plain of'a stream during the preceding winter; B, Typical schist "monument"__________ _______________ 52 X. A, Topography of the Kigluaik Mountains; B, Glacial topog­ raphy in the Kigluaik Mountains_________________ 62 XL Glacial cirque on east side of Mount Osborn___________ 62 XII. A, Channel cut by a stream flowing along the edge of the gla­ cier that formerly occupied Stewart River valley; B, Small cirque on south side of Thompson Creek valley_______ 63 FIGURE 1. Index map of southern Seward Peninsula, showing areas represented by detailed topographic and geologic maps___ 11 2. Folded beds in thick horizontal limestone stratum______ 29 3. Generalized section of gravel deposits north of Nome, on the third beach ____ _______ 41 4. Section of coastal-plain gravel deposits along Bourbon Creek__ 44 5. Diagrammatic cross section showing beaches near Nome___ 48 6. Geologic section, Anvil Mountain to Mount Osborn_______ 55 7. Diagram showing gold production of Seward Peninsula from 1897 to 1911_____________________________ 65 8. Map showing distribution of vegetation on Seward Peninsula__ 73 9. Sketch map of the vicinity of Nome, showing distribution of placers______ :_____ 78 10. Diagrammatic section of Anvil Creek valley, showing bench gravels___ _ _ . SO 11. Sketch map showing the position of pay streaks or old channels in the high-bench gravels at the head of Dexter Creek___ 102 12. Diagram showing concentration of gold on third beach __ 116 13. Diagrammatic section of beach placers _ 121 6 PREFACE. By ALFRED H. BROOKS. The investigation of the mineral resources of Seward Peninsula by the United States Geological Survey was begun in 1899 with a brief examination of the then newly discovered gold placers near Nome. During the succeeding five years geologic and topographic reconnaissance surveys (scale 4 miles to 1 inch) were carried over nearly the entire peninsula. There still remained a small area north of Norton Bay, which was surveyed in 1909, thus completing the reconnaissance mapping of the peninsula. Although these reconnaissance surveys have been of great value, it was recognized that a full understanding of the problems of strati- graphic and economic geology of the district could be achieved only by means of detailed surveys. Moreover, topographic maps of a larger scale were needed for the use of a community engaged in many engineering projects. Accordingly detailed topographic surveys (scale 1 mile to the inch, with 25-foot contours) of the Nome and Grand Central quadrangles were made in 1904 and of the Solomon and Casadepaga quadrangles in 1905. Detailed geologic surveys and investigations were made at Nome in 1905 and 1906 and at Solomon in 1907 and 1908. After the com­ pletion of the surveys of the Nome and Grand Central quadrangles it was found that many geologic problems concerning those areas were so complex as to defy solution unless the investigations were extended into adjoining fields, and therefore the publication of the report was deferred until the Solomon and Casadepaga quadrangles could be surveyed. The expectation that the information thus gained would help to solve the problems referred to was, however, only in part fulfilled. It was found that the stratigraphic results obtained in the Solomon region could be correlated with the geology of the Nome region only by surveying the intermediate area, a belt some 30 miles in width. Unfortunately the urgent need for investigations in other parts of Alaska, made it necessary to defer the making of any more detailed surveys in Seward Peninsula. These conditions 7 8 PREFACE. left but two courses open in regard to the results