STATE OF OREGON DEPARTMENT OF GEOLOGY AND MINERAL INDUSTRIES 1005 State Office Building Port1and, Oregon 97201 OPEN-FILE REPORT 0-83-2 GEOLOGY AND MINERAL RESOURCES OF 18 BLM WILDERNESS STUDY AREAS HARNEY AND MALHEUR COUNTIES, OREGON By Jerry J. Gray, Norman N. Peterson, Janine Clayton, and Gary Baxter Oregon Department of Geology and Mineral Industries The work was supported by the U.S. Department of Interior Bureau of Land Management Contract No. YA-553-CT1-1086 NOTICE The Oregon Department of Geology and Mineral Industries is publishing this paper because the subject matter is consistent with the mission of the department. To facilitate timely distribution of information, this paper has not been edited to our usual standards. CONTENTS EXECUTIVE SUMMARY ......................................................... 1 INTRODUCTION .............................................................. 3 General .............................................................. 3 Departmental Qua1ifications .......................................... 3 Contract ............................................................. 4 Purpose ......................................................... 4 Parameters ...................................................... 4 Deliverables ................................................... 4 Acknowl edgments ...................................................... 7 OFFICE RESEARCH AND ACTIVITIES ........................................ 8 General .............................................................. 8 Compilation of Geologic Maps ........................................ 8 Literature Search for Geophysical Data ............................... 8 Literature Search for Geothermal Data ................................ 9 Literature Search for Mines. Prospects. and Mineralization ........... 10 Literature Search for Geochemical Surveying Case Studies ............. 11 Mining Firm Interviews ............................................... 11 Computer System ...................................................... 11 FIELD SURVEYING ........................................................... 17 General .............................................................. 17 Pilot Study .......................................................... 17 Geochemical Sampling ................................................. 17 Field Checking of Geological Maps .................................... 21 Field Checking of Mines. Prospects. and A1 teration/Mineral ization .... 21 LABORATORY SUPPORT ........................................................ 22 General .............................................................. 22 Definition of Term "Sample" .......................................... 22 Sample Preparation ................................................... 22 Sample Preparation Steps ........................................ 22 Stream Sediments ................................................ 23 Soils .......................................................... 23 Rock Chips ...................................................... 24 Analytical Program ................................................... 24 Analytical Methods ................................................... 24 General ......................................................... 24 Decomposition Methods ........................................... 25 Instrumental Methods of Analysis ................................ 26 Specific Methods ................................................ 26 Qua1i ty-Control Program ........................................ 27 Petrographic Services ................................................ 28 GEOCHEMICAL DATA .......................................................... 29 General .............................................................. 29 Tabulated Assay and Site Data ........................................ 29 Sample Location Maps ................................................. 30 Random Resampl i ng .................................................... 30 Assay Data Summary by Sample Type and By All Samples ................. 31 Frequency Tab1 es and Histograms ...................................... 31 Stepwise Multiple Regression with Silver as the Dependent Variable ... 31 Least Squares Correlations and Scatter Graphs ........................ 34 Anomalous Value Thresholds ........................................ 34 Soi 1-Sampl e Prof i 1es ................................................. 38 Computer-Plotted Anomaly Overlays .................................... 38 WILDERNESS STUDY AREA SUMMARY REPORTS ..................................... 46 General .............................................................. 46 Owyhee Reservoir Area ................................................ 47 General ......................................................... 47 Geology ......................................................... 47 Stratigraphy .................................................... 48 Structure ....................................................... 50 Geophysical Data ................................................ 51 Mines. Prospects. and Mineral ized Areas ......................... 51 Geochemical Sampl i ng Results .................................... 51 Mineral Potential ........................................ 53 General .................................................... 53 Oil and gas ................................................ 53 Geothermal energy .......................................... 53 Metallic commodities ....................................... 54 Middle Owyhee Area ................................................... 54 General ......................................................... 54 Geology ......................................................... Stratigraphy .................................................... Structure ....................................................... Geophysical Data ................................................ Mines. Prospects. and Mineralized Areas ......................... Geochemical Sampling Results .................................... Mineral Potential ............................................... General .................................................... Oil and gas ................................................ Geothermal energy .......................................... Metallic commodities ....................................... Upper Owyhee River Area .............................................. General ......................................................... Geology ......................................................... Stratigraphy .................................................... Structure ....................................................... Geophysical Data ................................................ Mines, Prospects, and Mineralized Areas ......................... Geochemical Sampling Results .................................... Mineral Potential ............................................... General .................................................... Oil and gas ................................................ Geothermal potential ....................................... Metallic commodities ....................................... Trout Creek Area ..................................................... General ......................................................... Geology ......................................................... Stratigraphy .................................................... Structure ....................................................... Geophysical Data ................................................ Mines . Prospects. and Mineral i zed Areas ......................... Geochemical Sampling Results .................................... Mineral Potential ............................................... General .................................................... Oil and gas ................................................ Geothermal energy .......................................... Metallic commodities ....................................... Pueblo Mountains Area ................................................ 74 General ......................................................... 74 Geology ......................................................... 74 Stratigraphy .................................................... 75 Structure ....................................................... 78 Geophysical Data ................................................ 78 Mines. Prospects. and Mineralized Areas ......................... 78 Geochemical Sampling Results .................................... 80 Mineral Potential ........................................ 80 General .................................................... 80 Oil and gas ................................................ 80 Geothermal energy .......................................... 80 Metallic commodities ....................................... 82 Steens Mountain Area ................................................. 83 General ......................................................... 83 Geology ......................................................... 84 Stratigraphy .................................................... 84 Structure ....................................................... 86 Geophysical Data ................................................ 87 Mines. Prospects. and Mineralized Areas ......................... 87 Geochemical Sampling Results .................................... 87 Mineral Potential ..............................................