Mineral Land Assessment I Open File Report/1986 | Mineral Investigation of a Part of the Eagletail | Mountains Wilderness Study Area (AZo020o128), La Paz, Maricopa, and Yuma Counties, Arizona I I I I I I I ! - ! ! I ~~/~ UNITED STATES DEPARTMENT OF THE INTERIOR I irl MINERAL INVESTIGATION OF A PART OF THE EAGLETAIL MOUNTAINS WILDERNESS STUDY AREA (AZ-020-128), LA PAZ, MARICOPA, AND YUMA COUNTIES, ARIZONA I I by I Michael E. Lane I MLA 45-86 1986 I I I Intermountain Field Operations Center, Denver, Colorado I I UNITED STATES DEPARTMENT OF THE INTERIOR I Donald P. Hodel, Secretary BUREAU OF MINES I Robert C. Horton, Director I I PREFACE The Federal Land Policy and Management Act of 1976 (Public Law 94-579) requires the U.S. Geological Survey and the U.S. Bureau of Mines to conduct mineral surveys on certain areas £o determine the mineral values, if any, that may be present. Results must be made available to the public and be submitted to the President and the Congress. This report presents the results of a mineral survey of a part of the Eagletail Mountains Wilderness Study Area (AZ-020-128), La Paz, Maricopa, and Yuma Counties, Arizona. }| This open-file report summarizes the results of a Bureau of Mines wilderness study. The report is preliminary and has not been edited or reviewed for confoz~nity with the Bureau of Mines editorial standards. This study was conducted by personnel from the Branch of Mineral Land Assessment (MLA), Inter~nountain Field Operations Center, Building 20, Denver Federal Center, Denver, CO 80225. i I I CONTENTS I Summary .................................................................. 1 Introduction ............................................................. 1 I Geographic setting .................................................. 2 I Methods of evaluation ............................................... 2 Geologic setting ......................................................... 4 I Mining history ........................................................... 4 Energy resources ......................................................... 5 I Appraisal of sites examined .............................................. 5 I Conclusions .............................................................. 9 References ............................................................... I0 I ILLUSTRATIONS Plate I. Mine and prospect map of the Eagletail Mountains Study at I Area ........................................................ back I Figure i. Index map of the Eagletail Mountains Study Area ............. 3 2. Map showing oil and gas leases in and near the Eagletail I Mountains Study Area ........................................ 6 3. Map showing sample localities 19-52 ......................... 7 I 4. Mine map showing sample localities 32-36 .................... 8 I TABLES Table i. Sampled areas in and near the Eagletail Mountains Study I Area ........................................................ 11 2. Analytical and sample data for samples 1-65 taken in and near I the Eagletail Mountains Study Area .......................... 12 I I ii I I UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT ft foot (feet) I mi mile(s) ozlst troy ounce per short ton (2,000 pounds) I % percent I °C deEree Celsius I I i i? !|' i~i~ . iii I MINERAL INVESTIGATION OF A PART OF THE EAGLETAIL MOUNTAINS WILDERNESS I STUDY AREA (AZ-020-128), LA PAZ, MARICOPA, AND YUMA COUNTIES, ARIZONA by I Michael E. Lane, Bureau of Mines SUMMARY I In April and June 1985, the Bureau of Mines conducted a mineral I investiEation of a part of the 119,700-acre Eagletail Mountains Wilder~ess Study Area in La Paz, Haricopa, and Yuma Counties, southwestern Arizona, as I authorized by Public Law 94-579, October 21, 1976. Prospecting has occurred in and near the study area; there was no mininE activity at the time of this I investigation. Forty tons of manganese ore was mined from the Eagletail I mining district from an undetermined location. Sixty-five samples were taken, five from within the study area. Field I and sample data did not indicate any identifiable resources. INTRODUCTION I In April and June 1985, the Bureau of Hines, in a cooperative proEram I with the U.S. GeoloEical Survey (USGS), studied the mineral occurrences of a part of the Eagletail Mountains Wilderness Study Area (WSA), La Paz, Maricopa, I and Yuma Counties, Arizona, on lands administered by the Bureau of Land I ManaEement (BLM) Phoenix District Office. The WSA comprises 119,700 acres; the Bureau studied the 70,230 acres deemed preliminarily suitable for I inclusion in the National Wilderness Preservation System. "Study area" (SA) as used in this report refers only to the smaller area and is shown on plate I 1. The Bureau surveys and studies mines, prospects, and mineralized areas to I appraise reserves and identified subeconomi¢ resources. The USGS assesses the potential for undiscovered mineral resources based on reEional Ecological, and I I 1 I reconnaissance geochemical and geophysical surveys. This report presents the results of the Bureau of Mines study, which was completed prior to the USGS I investigation. The USGS will publish the results of their studies. A joint USGS-Bureau report, to be published by the USGS, will integrate and summarize I the results of both surveys. I Geographic setting The Eagletail Mountains SA, in eastern La Paz and Yuma and western I Maricopa Counties, southwestern Arizona, lles about 70 mi west of Phoenix and 7 mi south of Interstate I0 (fig. i). The area encompasses the Eagletail I Mountains, part of Cemetery Ridge, and the alluvial plain in between. Access I to the SA is by improved and unimproved roads off Interstate I0; a few unimproved roads extend to and into the study area. I Terrain is typical of the desert southwest; steep, jagged mountains rise above broad alluvial plains. Vegetation is sparse and consists mostly of I cacti, mesquite, palo verde, and small shrubs. I Methods of evaluation Bureau personnel reviewed literature concerning mining and geology of the I region. In addition, BLM records were reviewed for mining claim information, I patented claim locations, and oil and gas leases and lease applications. About 20 man-days were spent examining mines and prospects inside and I within approximately 1 mi of the SA boundary (pl. i). Surface and underground surveys were made by compass and tape method. Mines and prospects were mapped I and sampled. I Sixty-five grab, select, and chip samples were taken; five samples were from within the SA (table I). All samples were fire assayed for gold and I silver (table 2); selected samples were analyzed by semiquantitative emission I N. "\ ~u ! 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I I spectrographic methods for 40 elements. Some samples contained visible copper and manganese minerals and were analyzed by atomic absorption methods for I copper and manganese. Complete analytical data for all samples are available for public inspection at the Bureau of Mines, Intermountain Field Operations I Center, Building 20, Denver Federal Center, Denver, Colorado. I GEOLOGIC SETTING The study area is in the Basin and Range physiographic province. The I northwest-trending Eagletail Mountains and, to the south, the parallel Cemetery Ridge are composed of Cretaceous to Quaternary andesites, basalts, I turfs, and dikes and plugs of rhyolitic to andesitic composition. Quaternary I sand and gravel forms the alluvial fringes of the mountains and fills the broad valley between Cemetery Ridge and the Eagletail Mountains. Paleozoic I limestone crops out near the southeast boundary of the study area at the Double Eagle Mine. Isolated outcrops of Precambrian schist, granite, and I gneiss also occur in the southeast part of the SA. (See Wilson and others, I 1957; Wilson, 1960.) MINING HISTORY I The study area is in the Eagletail mining district where prospecting began in the 1860's and has been sporadic since. The only reported production