DEPARTMENT OF THE INTERIOR ALBERT B. FALL, Secretary UNITED STATES GEOLOGICAL SURVEY GEORGE OTIS SMITH, Director Bulletin 733 GEOLOGY OF THE YORK TIN DEPOSITS ALASKA BY EDWARD STEIDTMANN AND S. H. CATHCART WASHINGTON GOVERNMENT PRINTING OFFICE 1922 ADDITIONAL COPIES OF THIS PUBLICATION MAT BE PROCURED FROM THE SUPERINTENDENT OF DOCUMENTS GOVERNMENT PRINTING OFFICE WASHINGTON, D. C. AT 30 CENTS PER COPY CONTENTS. \ Page. Introduction_____ ___ 1 Scope of report- _ 1 Acknowledgments 1 Geography 2 Location and area _ 2 Topography _____ ___ . 2 j! Drainage________-___ a. ____ _ 3 Climate _-_____ _ _ _ 4 Rock weathering________ ________________ 5 Rock transportation_______________ ________ __ 7 Vegetation and animals____ ____ ____ 9 Accessibility___________ ..__ _ _ 10 Harbor______________,_____________________ 10 Trails_____________________________________ 11 Habitation __________________________________ 12 Industries________________________..____ __ 33 Previous exploration _ _ __ 13 General geology 15 Summary of geologic history _ _ ______ 15 Slate of the York region __________________________ 1C General characteristics __ ________________ _ 16 Contacfmetamorphisin _____ _____ _ ___ 17 Conditions of deposition _ ____________ ___ 17 Pre-Ordovician basalt and gabbro________ _____ 19 Limestone_______ _ _ ___ _ _ 19 Limestone of the York Mountains _________________ 20 Limestone of Cape Mountain _________________ _ 20 Structural relations of the slate and limestone ____ _ 22 Contact metamorphism ________________________ 22 Fosils and age_ _ _ ______ _ 23 ! Conditions of deposition _______________________ 29 Granite, associated dikes, and tin ores __________________ 30 : Amygdaloidal olivine basalt _ 31 Sequence of igneous intrusions _ ______ _ __ 31 Structure______________ __________________ 32 Topographic history ____________________________ 34 Mineralogy ________________.__________________ 36 Lost River area ____________ __________________ 44 Geographic features_____________________________ 44 General geology ___ _____ 45 Summary____________ __ _ ______ ___ 45 Limestone ___ ___ ___ ______ _ 46 v. Quartz porphyry dikes __ ___ _ _________ 48 Granite _____________________________*___ 49 Erosion____________________________________ 49 276046 IV CONTENTS. Lost River area Continued. Page. Prospects ____ __ _____________________ 51 Cassiterite Creek tin prospect ____________________ 51 General geologic relations of the tin deposits ________ 51 Limestone __ __________________ 51 Faults _______________________________ 53 Quartz porphyry dikes ______________________ 55 Breccia ___________________________'___ 56 Effects of the tin-bearing solutions on the quartz porphyry dikes ______________________________ 58 Effects of the tin-bearing solutions on the limestone ___ 61 Developments ___________________________ 63 Adit No. 3___________________________ 64 Adit No. 2____________________________ 66 Adit No. 1___________________________ 66 Randt extension tunnel___________________ 67 Workings on Greenstone lode________________ 69 Ida Bell tunnel________________________ 71 Probable tonnage of tin-bearing dike above the level of Cas­ siterite Creek___ ______________________ 72 Tin content of the Cassiterite dike_______________ 73 Probable extent of the tin deposits of the Cassiterite dike beneath the level of Cassiterite Creek____________ 73 Placer tin on Cassiterite Creek_ _______________ 74 Tin Creek tin prospect________________________ 74 Dolcoath tin-bearing dike_________________ ___ 76 Bessie and Maple antimony and lead claims.__________ 78 Yankee Girl lead and tin prospect__________________ 80 Other prospects _____ __________ 81 Wolframite-topaz lode_______________________ 81 Alaska Chief claim__ ____________________ 81 Idaho copper claim________________________ 81 Brooks Mountain __ 81 Geographic features_ _ _ _ 81 General geology 83 Summary_________ ____________________ 83 Slate__________________________________ 84 Limestone _ _ ___ _______.. 84 Granite_____________-_______________ __ 85 Prospects _____ _ _ _ _ 86 Read lead prospect _ _ _ _ _ 86 Luther lead prospect________ _____ ______ 86 Mineralizing solutions___ - _ _ ___ __ _ 87 Probability of finding tin and other minerals in commercial quan-' tities at Brooks Mountain_ _ __ _ _ 88 Potato Mountain _ 88 Geographic features______ _ 88 Rocks________________________________________ 89 Economic geology __ _ 89 Lode developments _ _ 90 Tin placers : 94 Cape Mountain 96 Geographic features_____ -_ ___.. _ Oil CONTENTS. V Cape Mountain Continued. Page. General geology ______________________________ 97 Sumniary__ _______________________ 97 Granite _ _ _____________ _ 98 Granite pegmatite___________________________ 99 Quartz veins ___________________________ 99 Limestone _________ __________________ 100 Alteration of the granite by tin-bearing solutions_________ 101 Summary of occurrence of tin at Cape Mountain____________ 101 Developments____ __________________________ 102 Production of tin ore _ _________ _ _ ___ 102 Placer tin ___________________________________ 102 Ear Mountain ____________________________________ 102 Geographic features _________________________ _ 102 General geology_______________-__.__________ 103 Summary___ __ _ ____ _ 103 Quartz-mica schist and associated basic intrusive rooks 105 Limestone _________________________-_____ 106 Granite______________________________ 106 Quartz-augite porphyry ______________,________ 108 Contact metamorphism_________ ; 108 Limestone ___________________-_______ - 108 Granite________L____ __________________ 109 Quartz porphyry dikes________________________ 109 Tin deposits__________________________________ 110 Developments _________________________________ 110 Black Mountain_________________ _____ __ ._____ 111 Location and general features______ _____________ 113 General geology _. 111 Summary __ _ __ ___ 111 Faults ________-_________________________ 112 Slate ___________________________________ 114 Pre-Ordovician basalt and gabbro ____________________ 114 Limestone____ _ ______ _ _______ __ 115 Granite______,_________..__________________ 116 Alteration of the limestone beds by the granite___________ 116 Quartz veins _ _ _ _ ___ __ 116 Quartz porphyry dikes ______ ,_________ 116 Amygdaloidal olivine basalt-_______ ____________ 117 Comparison of the tin deposits of the York region with the other tin de­ posits of the world________'______ __ ___ __ US Association with granite- _ _____ _______ _ 118 Composition of granite associated with tin deposits _______ 119 Kinds of rocks into which tin-bearing granites are intruded______ 119 1 Location of ores with reference to granite ____ 119 Age of tin deposits _ _____ 120 Classification of tin deposits________________________ 120 Rock alterations associated with tin deposits_____________ 321 Origin of the tin deposits of the York region_________________ 122 Tin deposits associated with granite___________________ 122 Tin minerals deposited from solutions after solidification of granite. 122 Character and source of solutions_______________________ 123 Sequence of the tin-bearing solutions__________________ 124 Suggestions on lode tin prospecting in the York region__________ 124 Index ____ _______ __ ____ __ _ ____________ 127 ILLUSTRATIONS. Page. PLATE I. Topographic and geologic reconnaissance map of York tin re­ gion, showing location of prospect and localities from which fossils have been collected__________ ________ 4 II. Frost cracks in slope wash east of Lost River _ 6 III. Surface features near the mouth of Lost River: A, Canyon near the mouth of Lost River; B, The sea terrace near Lost River and the York Mountains in the background- ___ 7 IV. A, Contorted Port Clearance limestone and sea cliffs west of Lost River; B, Sea cliffs and terrace east of Lost River___ 46 V. A, Workings on Cassiterite dike on east side of Cassiterite Creek and on the Greenstone lode; B, Lode workings and camp on Cassiterite Creek _______________ _ 47 VI. Mineralization of limestone, Cassiterite Creek: A, Polished sur­ face of altered limestone near Cassiterite lode; B, Thin sec­ tion of cassiterite vein in' limestone near Cassiterite lode__ 62 VII. Mineralization of " reef" limestone, Cassiterite Creek: A, Rough surface of " reef " limestone, near Cassiterite lode; B, Rough surface of " reef " limestone______-___ _____ 63 VIII. A, Cassiterite and wolframite replacing Cassiterite dike; B, Cassiterite vein from Ida Bell dike_______________ 72 I.. Concentric bands or orbules near limestone contact at Tin Creek: A, Orbule produced by contact metamorpnism; B, Re­ verse side of orbule shown in A: C, Maximum orbule, diam­ eter 8 inches; D, Irregular orbules__,____________ 73 X. Geologic map and sections of Brooks Mountain_________ 82 XI. A, Arctic coastal flats, Cape Prince of Wales, and Kingegan Mis­ sion from Cape Mountain; B, Upland surface (1,000-foot ter­ race) at Cape Mountain______________________ 96 XII. Geologic map of Black Mountain__________________ 112 FIGUEE 1. Outline map of Seward Peninsula showing location of York region ________________________________ 2 2. Sketch of the coast from Cape York to Cape Prince of Wales, Alaska______________'_________________ 4 3. Frost-crack pattern _________________________ 8 4. Profile section along west bank of Lost River from mouth / northward _________________________ _ _ 46 5. Geologic sketch map of Cassiterite Creek and vicinity____ 52 6. Idealized sketch showing mineralization of limestone -at Cas­ siterite Creek tin prospect.___ ___ _ ______ 59 7. Plan of lode workings