Geology and uranium deposits of the Shinarump conglomerate of Nakai Mesa, Arizona and Utah Item Type text; Thesis-Reproduction (electronic) Authors Grundy, Wilbur David, 1929- Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 03/10/2021 21:24:56 Link to Item http://hdl.handle.net/10150/551207 GEOLOGY AMD URANIUM DEPOSITS 0$’ THE SHINARUMP CONGLOivERATE OF NOKAI MESA, ARIZONA AND UTAH by Wilbur David. Grundy A Thesis submitted to the faculty of the Department of Geology in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in the Graduate College, University of Arizona 1953 Approved: Director of Thesis ^ D a t e V This thesis has been submitted in partial fulfillment of requirements for an advanced degree at the University of Arizona and is deposited in the Library to be made available to borrowers under rules of the Library. Brief quotations from this thesis are allowable without special permission, proviaed that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the dean of the Graduate College when in their judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author. SIGHED: TABLE OF CONTENTS CHAPTER ' PAGE INTRODUCTION . ....................................... 1 General Statement ................................... 1 Acknowledgments................ .3 Location and Accessibility........ ............. 3 Climate ............................................. 5 Topography and Drainage ............................. 6 Previous Investigations . ........................... 7 1 METHODS OF INVESTIGATION . Lithologic Studies ..... Procedure ............ Sandstone specimens to (O (O <o Gravel specimens .......................... 10 Cross-stratification Studies ................ .... 12 General ................................ 12 Procedure....................................... 12 2 GENERAL GEOLOGY OF NOEAI M E S A ............ .......... 16 G e n e r a l ............................................. 16 Sedimentary Rocks ........................ ..... 16 Cutler formation .............................. 16 Organ Rock t o n g u e ....................... 17 De Chelly sandstone ...................... 19 Hoskinnini tongue ........................ 20 Moenkopi formation ............................ 21 Shinarump conglomerate ........... ...... 24 Chinle f o r m a t i o n .............................. 25 Structural Geology of Nokai Mesa ........... 27 General . .......................... ...... 27 J o i n t i n g ................ 28 F a u l t i n g ....................................... 28 Time of deformation.......................... 29 3 GEOLOGY OF SHINARUMP CONGLOMERATE AT NOKAI MESA . 30 General Statement ................................... 30 General Appearance................................... 30 Distribution and Thickness.......................... 51 Age of the Shinarump C o n g l o m e r a t e .................. 51 Location of Late TTiassic U p l i f t .................... 33 Late Tfiassic Climate ............................... 35 Pre-conglomerate Surface ............................. 36 Basal C o n t a c t ....................................... 37 Bleached zone in the Moenkopi formation .... 38 Cause of bleaching.................... 39 TABLE OF CONTENTS (CQRTD.) CHAPTER PAGE Erosional unconformity ........................... 41 Tine r e p r e s e n t e d ........................... 43 Amount of erosion ......................... 43 Upper Contact ............................ ..... 44 Original Sedimentary Structures ...................... 45 Stratification ................................. 45 Cross-stratification .................... 46 Lower zone ................................. 49 Middle z o n e ................................. 51 Upper z o n e ................................. 54 Interpretation of zoning ......................... 54 Small scale structures ......................... 58 Ripple m a r k s ............................ • 58 Li neat ion ................................. 59 Unconsolidated Rock deformation ...... 59 Sand c o n c r e t i o n s ........................... 60 Lithology of Shinarump Conglomerate at Nokai Mesa . 61 G e n e r a l ......................................... 61 Sandstones....................................... 62 Conglomerates ................................... 66 Quartz Pebble conglomerates ................ 66 Mud Pellet conglomerates .................. 67 S'naly clay l e n s e s ............................... 71 Fossil w o o d ..................................... 71 4 SHniARUIP CONGLOMERATE AT OTHER A R E A S .............. 73 General............................................... 73 S c o u r i n g ............................................. 73 Cross-stratification............................. 75 Gravels............................................... 75 5 URANIUM DEPOSITS IN THE SHINARUMP CONGLOMERATE . 79 General............................................... 79 Mineralogy of Deposits ............................... 80 Controls of Mineralization ........................... 80 Clay as a mineralizing f a c t o r ................... 81 Wood as a mineralizing f a c t o r .................. 82 Tectonic controls ............................... 83 Origin of Uranium De p o s i t s ........................... 84 Syngenetic theory ............................... 85 Concentration by meteoric circulation .......... 85 Hydrothermal theory ............................. 86 Emplacement of Ore in C h a n n e l s ...................... 86 Summary of Ore Controls .................. ..... 88 FIGURES NUMBER PAGE 1 Index Map 4 2 Types of Cross-stratification in three Zones 48 3 Lower Zone Cross-strata Trends 50 4 Middle Zone Cross-strata Trends 53 5 Upper Zone cross-strata Trends 55 TABLES NUMBER : PAGE I Middle Zone Cross-strata Trends 52 II Upper zone Cross-strata Trends 56 III Mechanical Analysis of Drill Core N1— Channel Outcrop E, Mokai Mesa 64 III A- Mechanical Analysis of Ten Foot Samples— Southwest Nokai Mesa 65 17 Pebble Counts for Nokai Mesa Area 68 V Composition of Pebbles— Nokai Mesa 69 VI Cross-stratification Date for other Areas 76 VII Pebble Counts for other Areas 78 VIII Composition of Pebbles for other Areas 78 PLATES NUMBER PAGE I Geologic Sketch Map of Mokai Mesa Area, Arizona and Utah in pocket II General Stratigraphic Column of Nokai Mesa Area in pocket III A Normal fault at Nokai Mesa 89 III B Channel outcrop B. 89 IV A Bleached zone in Moenkopi formation 90 IV B Joint control of thickness of bleached zone 90 V A Channel outcrop D 91 V B Southern outcrop of channel at Monument N o . 2 Mine 91 VI A Mineralized trough of channel outcrop E. 92 VI B Trash pocket 92 VII A Planar cross-strata 93 VII B Surface viev: of trough cross-strata 93 VIII A Evidence of scouring of Shlnarump conglomerate 94 VIII B Shaly parting in clay galls 94 IX A Unconsolidated rock deformation in Shlnarump cross-strata 95 IX B Sand concretions. 95 X A Quartz pebble conglomerate lens 96 X B Mud pellet conglomerate 96 XI Panorama of Nokai Mesa 97 INTRODUCTION General Statement This thesis presents the results of a study of the Shinarump con­ glomerate of Nokai Mesa, Arizona and Utah, an area which lies about 15 miles west of Monument Valley. It includes comparisons with the Shinarump conglomerate of other areas in northern Arizona and southern Utah. Special emphasis is placed on the occurrences of uranium in the unit in an attempt to determine relationships between sedimentary structures and uranium mineralization. The chief purpose of this work, therefore, is to obtain detailed information on the lithology and sedimentary structures of the Shinarump conglomerate. These features are believed to have con­ trolled the deposition of the uranium minerals at Nokai Mesa. Such studies should contribute substantially to an understanding of the ore deposits. The geologic field work was conducted during the summer and in the latter part of December of 1952. The studies included detailed examinations of the uranium deposits for the purposes of determining which features associated with these minerals had a critical influence on their localization. Careful attention was given to cross-stratification in the Shinarump conglomerate. Dip and dip direction measurements of the cross-strata were made to determine the nature of the currents 2 responsible for deposition of the formation and to determine, if possi­ ble, relationships between the mineral deposition and the cross- stratification. Stratigraphic sections were measured in the Nokai Mesa area and representative lithologic samples were collected for later laboratory study. A geologic map of Nokai Mesa showing the areal distribution of the rock formations and structures was prepared, based on aerial photographs (flown by Aero Service Corp., 1951, scale 1:22,000). In addition to the detailed studies of the Shinarump conglomerate on Nokai Mesa, reconnaissance examinations were made in several other selected areas. This work involved cross-stratification studies and measurements of the thickness of the Shinarump,