Geology and Description of Thorium and Rare-Earth Deposits in the Southern Bear Lodge Mountains, Northeastern Wyoming

l^ft PER COVER PHOTOGRAPHS 1 . Asbestos ore 8. Aluminum ore, bauxite, Georgia 1 2 3 4 2. Lead ore, Balmat mine, N. Y. 9. Native copper ore, Keweenawan 5 6 3. Chromite-chromium ore, Washington Peninsula, Mich. 4. Zinc ore, Friedensville, Pa. 10. Porphyry molybdenum ore, Colorado 7 8 5. Banded iron-formation. Palmer, 11. Zinc ore, Edward, N. Y. Michigan 12. Manganese nodules, ocean floor 9 10 6. Ribbon asbestos ore, Quebec, Canada 13. Botryoidal fluorite ore, 11 12 13 14 7. Manganese ore, banded Poncha Springs, Colo. rhodochrosite 14. Tungsten ore. North Carolina Geology and Description of Thorium and Rare-Earth Deposits in the Southern Bear Lodge Mountains, Northeastern Wyoming By MORTIMER H. STAATZ GEOLOGY AND RESOURCES OF THORIUM IN THE UNITED STATES GEOLOGICAL SURVEY PROFESSIONAL PAPER 1049-D A description of the size, mineralogy, chemical composition, economic geology, and geologic setting of the thorium and rare-earth veins and newly discovered large disseminated deposits UNITED STATES GOVERNMENT PRINTING OFFICE, W AS H I NGTON : 1 983 UNITED STATES DEPARTMENT OF THE INTERIOR JAMES G. WATT, Secretary GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Congress Cataloging in Publication Data Staatz, Mortimer Hay, 1918- Geology and description of thorium and rare-earth deposits in the southern Bear Lodge Mountains, northeastern Wyoming (Geological Survey Professional Paper 1049-D) Bibliography: 52 p. Supt. of Docs. No.: I 19.16:1049-D 1. Thorium ores Wyoming Bear Lodge Mountains. 2. Earth, Rare Wyoming Bear Lodge Mountains. I. Title. II. Series. III. Series: Geological Survey Professional Paper 1049-D QE390.2.T45S73 553.4'93 81-607092 AACR2 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Page Page Abstract ................................... Dl Pseudoleucite Dorohvrv . D22 Introduction ................................ 2 22 Location and accessibility .................. 2 23 Geography .............................. 2 24 Previous work ........................... 4 25 Present work and acknowledgments ......... 5 A oro 25 Rock units .................................. 5 Granite (Precambrian) ..................... 7 White River Formation (Oligocene) ............... 26 Dead wood Formation (Late Cambrian and Early Ogallala Formation (late Miocene and Pliocene) ..... 27 Ordovician) .......................... */ 28 Whitewood Limestone (Late Ordovician) ...... 11 28 Pahasapa Limestone (Early Mississippian) .... 11 Structure and its relation to igneous bodies ........... 29 Minnelusa Sandstone (Pennsylvanian and Early Permian) ............................ 12 32 Opeche Formation (Permian) ................ 12 A/^ific 32 Minnekahta Limestone (Permian) ............ 13 32 Spearfish Formation (Permian and Triassic) .... 13 33 Sundance Formation (Middle and Late Jurassic) 14 Chemical composition ...................... 40 Morrison Formation (Late Jurassic) .......... 15 Economic geology ......................... 42 Lakota Formation (Early Cretaceous) ......... 15 43 Tertiary intrusive and volcanic rocks ......... 16 43 Introduction ......................... 16 \lineralo£rv 46 Phonolite and trachyte ................. 17 48 Latite ............................... 19 50 Syenite and nepheline syenite ........... 20 Lamprophyre ........................ 20 References cited ................................. 51 ILLUSTRATIONS [Plates are in pocket] PLATE 1. Geologic map of the southern Bear Lodge Mountains. 2. Radiometric and element content maps of the southern Bear Lodge Mountains. FIGURE 1. Index map showing location of area mapped ........................................................... D3 2. Generalized columnar section of the Paleozoic and Mesozoic rocks ...................... 3-5. Photographs showing: 3. Granite along Ogden Creek ............................................... ............... 7 4. Opeche Formation between the Minnekahta Limestone and the Minnelusa Sandstone ............... 13 5. Several trachyte intrusives ............................................... ............... 16 6. Diagram of relations between K2O, Na-sO, and CaO in Tertiary intrusive rocks ............. ............... 19 7. Diagram of relation of MgO to total iron oxide in Tertiary intrusive rocks ................. ............... 19 8-11. Photographs showing: 8. Tertiary intrusive rocks .................................................. ............... 21 9. Ogallala Formation ..................................................... ............... 28 10. Moat formed along landslide scarp ......................................... ............... 28 11. Sheep Mountain ........................................................ ............... 29 12. Geologic map and section of Sheep Mountain ....................................... ............... 30 13. Photographs of two veins ............... 33 14. Graphs of relation of thorium content to radioactivity .................................................... 45 15. Graph of relation of uranium to total rare earths in the disseminated deposits ................................. 49 in IV CONTENTS TABLES TABLE 1. Chemical analyses and normative compositions of Precambrian granite ........................................... D8 2. Chemical analyses and normative compositions of Tertiary intrusive rocks ........................................ 18 3. Gamma-ray spectrometric analyses of carbonatites ........................................................... 23 4. Semiquantitative spectrographic analyses of carbonatites ..................................................... 24 5. Dimensions and attitudes of the veins ..................................................................... 32 6. Mineralogy of the thorium- and rare-earth-bearing veins ....................................................... 35 7. Chemical analyses of samples from veins ................................................................... 37 8. Mineralogy of the disseminated deposits ................................................................... 47 STRATIGRAPHIC SECTIONS SECTION 1. Deadwood Formation ............................................................................. D10 2. Ogallala Formation (part) .......................................................................... 27 3. Ogallala Formation (part) .......................................................................... 27 GEOLOGY AND RESOURCES OF THORIUM IN THE UNITED STATES GEOLOGY AND DESCRIPTION OF THORIUM AND RARE-EARTH DEPOSITS IN THE SOUTHERN BEAR LODGE MOUNTAINS, NORTHEASTERN WYOMING By MORTIMER H. STAATZ ABSTRACT The Bear Lodge Mountains are a small northerly trending range ap oxides. Rare earths and thorium occur in the minerals monazite, proximately 16 km northwest of the Black Hills in the northeast cor brockite, and bastnaesite. Thorium content of 35 samples ranged ner of Wyoming. Thorium and rare-earth deposits occur over an area from 0.01 to 1.2 percent, and the total rare-earth content of 21 of 16 km2 in the southern part of these mountains. These deposits oc samples from 0.23 to 9.8 percent. Indicated reserves were calculated cur in the core of the Bear Lodge dome in a large multiple intrusive to a depth of one-third the exposed length of the vein. Inferred body made up principally of trachyte and phonolite. Two types of reserves lie in a block surrounding indicated reserves. Indicated deposits are recognized: disseminated deposits and veins. The reserves of all veins are only 50 t of ThO2 and 1,3601 of total rare- disseminated deposits are made up of altered igneous rocks cut by earth oxides; inferred reserves are 250 t of ThO2 and 6,8101 of total numerous crisscrossing veinlets. rare-earth oxides. The disseminated deposits contain thorium and rare-earth minerals The Bear Lodge dome, which underlies the greater part of this area, in a matrix consisting principally of potassium feldspar, quartz, and is formed by multiple intrusive bodies of Tertiary age that dome up iron and manganese oxides. Total rare-earth content of these deposits the surrounding sedimentary rocks. In the southern part of the core, is about 27 times that of the thorium content. the younger intrusive bodies surround and partly replace a granite of The general size and shape of the disseminated deposits were Precambrian age. This granite is approximately 2.6 b.y. old. The outlined by making a radiometric map using a scintillation counter of sedimentary rocks around the core are (from oldest to youngest): the entire Bear Lodge core, an area of approximately 30 km2. The Deadwood Formation of Late Cambrian and Early Ordovician age, most favorable part of this area, which was outlined by the 40 count's Whitewood Limestone of Late Ordovician age, Pahasapa Limestone (count-per-second) isograd on the radiometric map, was sampled in of Early Mississippian age, Minnelusa Sandstone of Pennsylvanian detail. A total of 341 samples were taken over an area of 10.6 km2 and and Early Permian age, Opeche Formation of Permian age, Min- analyzed for as many as 60 elements. Rare earths and thorium are the nekahta Limestone of Permian age, Spearfish Formation of Permian principal commodities of interest in these deposits. Total rare-earth and Triassic age, Sundance Formation of Middle and Late Jurassic content of these samples ranged from 47 to 27,145ppm (parts per age, Morrison Formation of Late Jurassic age, and the lower part of million), and the thorium content from 9.3 to 990 ppm. The amount of the Lakota Formation of Early Cretaceous age. In places,

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