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Igneous Dikes of the Eastern Uinta Mountians Utah and Colorado

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Igneous Dikes of the Eastern Uinta Mountians Utah and Colorado IGNEOUS DIKES OF THE EASTERN UINTA MOUNTAINS, UTAH AND COLORADO By Howard R. Ritzma UTAH GEOLOGICAL AND MINERAL SURVEY a di vision of Utah Department of Natural Resources Special Studies 56 August 1983 STATE OF UTAH Scott M. Matheson, Governor DEPARTMENT OF NATURAL RESOURCES Temple A. Reynolds, Executive Director UTAH GEOLOGICAL AND MINERAL SURVEY Genevieve Atwood, Director BOARD Kenneth R. Poulson, Chairman. .. Brush Wellman, Incorporated Laurence H. Lattman, Vice Chairman. .. University of Utah James H. Gardner ............................................. University of Utah Ro bert P. Blanc . Getty Oil Jo Brandt. .. Public-at-Large Elliot Rich. .. Utah State University E. Peter Matthies ....................................... Sharon Steel Corporation Ralph A. Miles, Director, Division of State Lands .................... ex officio member UGMS EDITORIAL AND ILLUSTRATIONS STAFF Klaus D. Gurgel ........................................................ Editor Nancy A. Close, L. Angeloff Sapienza ................................. Editorial Staff James W. Parker, Kent D. Brown, Jessie S. Roy. .. Cartographers IGNEOUS DIKES OF THE EASTERN UINTA MOUNTAINS Sentinel Rock, large dike outcrop, seen from above with view to east into Gilbert Creek Basin. Fault zone into which dike is intruded is marked by line of vegetation to left (north) oflake (proposed name, Steppingstone Lake). IGNEOUS DIKES OF THE EASTERN UINTA MOUNTAINS, UTAH AND COLORADO By Howard R. Ritzma UTAH GEOLOGICAL AND MINERAL SURVEY a division of Utah Department of Natural Resources Special Studies 56 August 1983 CONTENTS ABSTRACT .............................................................................. 1 INTRODUCTION. .. 1 MAPPING, SAMPLING AND ANALYTICAL WORK . .. 1 DESCRIPTION OF OCCURRENCES. .. 2 General ............................................................................... 2 Description of Outcrop Areas (West to East) ..... .. 4 Gunsight Pass. .. 4 Gilbert Peak and Gilbert Creek Basin .................................................... 4 Chepeta Lake ....................................................................... 6 Rose Ridge ......................................................................... 6 Deadman Lake ...................................................................... 7 Lakeshore Basin ... .. 8 Lodore Canyon . .. 9 PETROGRAPHY ....................................................................... 10 General Descriptions. .. 10 ASSAyS ............................................................................... 12 Titanium Content ..... :............................................................... 13 GEOCHRONOLOGY. .. 14 REGIONAL STRUCTURAL IMPLICATIONS. .. 15 Geophysics . .. 15 Strike-slip Faulting Within Uinta Mountains. .. 18 CONCLUSIONS ........................................................................ 18 LITERA TURE CITED . .. 23 ILLUSTRATIONS Figure 1. Index map showing location of dike outcrops. ......................................... 3 Figure 2. Map of Gunsight Pass, Gilbert Creek Basin, and Gilbert Peak localities. .................... 5 Figure 3. Map of Chepeta Lake and Rose Ridge localities. .. 7 Figure 4. Map of Deadman Lake and Lakeshore Basin localities. .................................. 8 Figure 5. Diagrammatic section of outcrops in headwall of Lakeshore Basin. .. 9 Figure 6. Graph showing range of dates obtained from samples of dike rocks. .. 15 Figure 7. Map showing possible structural offsets along trace of dike. ............................. 16 Figure 8. Photographs - Gilbert Peak and Gilbert Creek Basin ................................... 19 Figure 9. Photographs - Deadman Lake - Gabbro Pass. .. 20 Figure 10. Photographs - Gabbro Pass and Lakeshore Basin. ..................................... 21 Figure 11. Photographs - Lakeshore Basin . .. 22 TABLES Table 1. Assays of Samples ................................................................ 12 IGNEOUS DIKES OF THE EASTERN UINTA MOUNTAINS, UTAH AND COLORADO ByHOWARDR.RITZMAi ABSTRACT and samples brought in by prospectors and later Gabbro and diorite dikes of early Paleozoic age in­ from personal reconnaissance in the field. trude the Precambrian sediments of the eastern The location of this dike was shown in general Uinta Mountains from Kings and Gilbert Peaks, fashion on the northeast quarter of the state geologic Utah, eastward for 76 miles to Lodore Canyon, map (Stokes and Madsen, 1961) from information Colorado. Five outcrop areas are in Utah and one in furnished by the Untermanns. Mention of the dike Colorado. All are small in areal and linear extent as "gabbroid" was also made in Utah Geological and generally inconspicuous. and Mineralogical Survey Bulletin 72 (Untermann The dikes are intruded into a WNW to ESE­ and Untermann, 1964, p. 21, 71) and its extent pro­ trending fault and fracture zone which appears to jected westward based on the find in the Whiterocks have been broken into segments by post-intrusion River by the writer. The Untermanns also made strike-slip faulting with left-lateral displacement. brief mention of the dike in a later publication Field examination and assays of samples show (1972, p. 137) and exhibited samples of it in the scant mineralization associated with the intrusive museum at Vernal. A sample of dike rock furnished episode. Assays of dike rock show anomalous to the Utah Geological and Mineral Survey by the amounts of Ti02, an average of 3.7 percent for 26 Untermanns in 1972 was subsequently dated as 453 samples. Quartzite and shales in contact with the ± 17 m.y. (Ritzma, 1974, p. 95). dikes and associated fault gouge are only slightly Studies undertaken to evaluate the mineral poten­ mineralized but do show some consistent titanium tial of the High Uintas Primitive Area resulted in enrichment. U. S. Geological Survey Bulletin 1230-1 Known outcrops of the dikes in Utah occur ( Crittenden, Wallace and Sheridan, 1967). Field within the easternmost part of the High Uintas work for this study, which figured in classification Primitive Area and extend for 25 miles across an of the area as "primitive," was conducted during area proposed for classification as wilderness. The 1965 and 1966. In the bulletin, Plate 1, a reconnais­ dikes do not appear to have potential economic sance geologic map of the primitive area, lists mafic value that would affect classification of the lands in dikes in the explanation and shows two such dikes question as primitive or wilderness in character. outcropping on the eastern edge of the area. The INTRODUCTION text of the bulletin does not describe the dikes and In the early 1950s the writer found a small water­ contains several statements that "bedrock within rounded cobble of fine-crystalline, dark, igneous the primitive area consists entirely of sedimentary rock in the bed of the Whiterocks River on the rocks" (p. 1) and "complete absence of igneous south flank of the Uinta Mountains. Since it was rocks in the area" (p. 20). One assay, however, is then thought that there were no igneous rocks in described as having come from "hornfels adjoining. the Uintas, it was assumed that the rock had been dike" (p. 19). artificially introduced into the river gravels. The site Based on the mapping of Crittenden, Wallace and of the find was a popular camp ground, a circum­ Sheridan (1967, Plate 1) and unpublished mapping stance that reinforced the assumption. of the Utah Geological and Mineral Survey, the Some years later this find was mentioned to then-known dike outcrops in the Uinta Mountains Ernest and Billie U ntermann, curators of the Utah were shown on Hintze's Geologic Map of Utah Field House of Natural History museum in Vernal, (1980). and the writer was pleased to learn that the Unter­ MAPPING, SAMPLING AND manns had encountered a previously unmapped ig­ ANALYTICAL WORK neous dike in the eastern Uintas, first from reports Since 1976 the Utah Geological and Mineral iFormerly chief, UGMS Petroleum Section; presently consulting Survey has investigated occurrences of igneous geologist in Salt Lake City. rocks and associated mineralization in the eastern 2 Utah Geological and Mineral Survey, Special Studies 56, 1983 Uinta Mountains. The work was undertaken for greatly facilitated by unusually warm and dry four reasons: to determine the extent of igneous summer weather in 1981 and light snow cover in rocks in the eastern Uintas, to provide information the previous winter. Areas above 11,000 feet were in response to proposals that large additional areas almost devoid of snow, possibly to a degree not in the Uinta Mountains be designated as known in half a century or more. wilderness, to resolve the differences in information A sample of the Lodore Canyon, Colorado dike previously cited in U.S. Geological Survey Bulletin was obtained by Michael L. Perry, formerly 1230-1, and to provide accurate location of the director, Dinosaur Natural History Museum, Utah dikes for the planned revision of the state geologic Division of Parks and Recreation, Vernal, and map. In the course of the investigation, radiometric assays are included in this report. Petrographic work dating indicated that the dikes are about the same was performed by Lewis M. Downey, Salt Lake age as early Paleozoic, diamond-bearing, kimberlite City. Assays were performed by Rocky Mountain diatremes discovered in recent years in southeast Geochemical Laboratories, West Jordan, Utah. Wyoming. Aside from the contemporaneous intru­ sive age, relationship of the two appears to be DESCRIPTION OF OCCURRENCES remote. General In 1976
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