MINERAL RESOURCES OF THE SWANSEA WILDERNESS STUDY AREA, LA PAZ AND MOHAVE COUNTIES, ARIZONA By Richard M. Tosdall, Robert G. Eppinger2, H. Richard Blank, Jr.2, Daniel H. Knepper, Jr.2, Andrea J. Gallagher2, James A. Pitkin2, and Stephanie L. Jones1 U.S. Geological Survey and George S. Ryan2 U.S. Bureau of Mines U.S. Geological Survey Open-File Report 90-0521 Prepared by the U.S. Geological Survey and the U.S. Bureau of Mines for the U.S. Bureau of Land Management This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature. Any use of trade names is for descriptive purposes only and does not imply endorsement by the U.S. Geological Survey 'Menlo Park, CA 94025 2Denver, CO 80225 1990 STUDIES RELATED TO WILDERNESS Bureau of Land Management Wilderness Study Areas The Federal Land Policy and Management Act (Public Law 94-579, October 21, 1976) requires the U.S. Geological Survey and the U.S. Bureau of Mines to conduct mineral surveys on cenain areas to 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 the Swansea Wilderness Study Area (AZ-050415A), La Paz and Mohave Counties, Arizona. 2 CONTENTS Summary 5 Abstract 5 Character and setting 5 Identified resources 6 Mineral resource potential 7 Introduction 7 Location and physiography 7 Previous work 7 Methods of study 8 Acknowledgments 8 Appraisal of identified resources 8 Methods of investigation 8 Mining history 8 Oil and gas 9 Appraisal of sites examined 9 Conclusions 10 Assessment of mineral resource potential 10 Geology 10 Geochemistry 11 Introduction 11 Methods 11 Results 11 Interpretation 12 Geophysical studies 13 Aeromagnetics and gravity 13 Remote sensing 16 Radioelement distribution 17 Mineral resource assessment 18 Base and precious metals 18 Manganese 18 Uranium and vanadium 18 Oil and gas 19 Sand and gravel 19 References cited 19 Appendixes 22 Definition of levels of mineral resource potential and certainty of assessment 23 Resource/reserve classification 24 Geologic time chart 25 FIGURES 1. Index map showing location of the Swansea Wilderness Study Area, La Paz and Mohave Counties, Arizona 6 2. Map showing mineral resource potential and generalized geology of the Swansea Wilderness Study Area, La Paz and Mohave Counties, Arizona 26 3. Geochemical anomalies from stream-sediment, heavy-mineral concentrate, and rock samples from the Swansea Wilderness Study Area, La Paz and Mohave Counties, Arizona 14 4. Aeromagnetic anomaly map of the Swansea Wilderness Study Area, La Paz and Mohave Counties, Arizona 16 5. Bouguer gravity anomaly map of the Swansea Wilderness Study Area, La Paz and Mohave Counties, Arizona 17 3 TABLE 1. Summary statistics for elements found in anomalous concentrations in stream-sediment and heavy-mineral concentrate samples in the Swansea Wilderness Study Area, Arizona 15 4 Mineral Resources of the Swansea Wilderness Study Area, La Paz and Mohave Counties, Arizona By Richard M. Tosdal, Robert G. Eppinger, H. Richard Blank, Jr., Daniel H. Knepper, Jr., Andrea J. Gallagher, James A. Pitkin, and Stephanie L. Jones U.S. Geological Survey George S. Ryan U.S. Bureau of Mines SUMMARY corner of the study area has low potential for manganese. Areas of low potential for uranium and vanadium are found Abstract in the Tertiary sedimentary and volcanic rocks in the northern and southeastern parts of the study area. The entire Swansea The Swansea Wilderness Study area (AZ-050-015A) lies Wilderness Study Area has no resource potential for oil and gas in the Rawhide and Buckskin Mountains, west-central Ari- and sand and gravel. zona, about 20 mi east of Parker, Ariz. At the request of the U.S. Bureau of Land Management, mineral surveys of ap- Character and Setting proximately 15,755 acres were done by the U.S. Geological Survey and U.S. Bureau of Mines to assess its mineral re- The Swansea Wilderness Study area (AZ-050-015A) sources (known) and mineral resource potential (undiscov- ered). In this report, the study area refers to only that part of covers approximately 15,755 acres in La Paz' and Mohave the wilderness study area for which a mineral survey was Counties, west-central Arizona, about 20 mi east of Parker, requested by the U.S. Bureau of Land Management Ariz. (fig. 1). The study area straddles the Bill Williams Mining and prospecting activity has occurred in or adja- River, which divides the Rawhide Mountains on the north cent to the Swansea Wilderness Study Area in the Swansea, from the Buckskin Mountains on the south. Elevations in Mesa, and Owens mineral districts. Copper, silver, and lesser the study area range from about 600 ft along the Bill Wil- quantities of gold, lead, zinc, and manganese have been pro- liams River to 1,600 to 1,700 ft at the highest point on duced from mines in these districts. Metals have been recov- Black Mesa, north of the nver, and at the crest of the Buck- ered from deposits along the Buckskin-Rawhide detachment skin Mountains south of the river. fault and subsidiary high- and low-angle normal faults (Swansea The study area lies in the northwest-trending belt of and Mesa mineral districts) and along northwest-striking high- metamorphic core complexes in west-central Arizona (Rehrig angle faults that cut mylonitic gneiss and schist (Owens min- and Reynolds, 1980). In these complexes, mid-crustal and eral district). There are no identified resources in the study area. deeper rocks were tectonically transported to the surface Moderate and high potential for base and precious met- along shallow-dipping normal faults or detachment faults als (copper, lead, zinc, gold, silver) in the study area exists in during a period of extensional tectonism in the late Oligo- areas along northwest-striking high-angle faults in the north- ce,ne and Miocene (Davis and others, 1980; Spencer and ern part of the study area, along high- and low-angle faults in Reynolds, 1986; Davis, 1988) (see appendixes for geologic the lower-plate terrane south of the Bill Williams River, and time chart). The detachment fault in the study area is the along the Buckskin-Rawhide detachment fault and its upper- Buckskin-Rawhide detachment of Spencer and Reynolds plate faults on the south, northeast, and northwest margins of (1986, 1989), which crosses the northern part of the study the area; low potential exists in the south-central area. Part of area and crops out discontinuously along the south border Black Mesa in the northern part of the study area has high of the study area (fig. 2). The detachment fault divides the potential for manganese, whereas an area in the southeast ' La Paz County was created by the Arizona Legislature effective January 1,1983, from what was the northern half of Yuma County. 5 bedrock geology of the area into two parts, an extended and basins, and younger high-angle faults are important con- highly faulted upper plate of Proterozoic, Paleozoic, Meso- trols on the distribution of mineral resources in the study zoic, and Tertiary metamorphic, igneous, and sedimentary area (Spencer and Welty, 1985, 1989). Mineral exploration rocks, and a lower plate of Tertiary mylonite and mylonitic in western Arizona and southeastern California has focused gneiss that was derived from Proterozoic, Paleozoic, Meso- on these geologic terranes, and some deposits and prospects zoic, and Tertiary metamorphic, igneous, and sedimentary are known (Sherborne and others, 1979; Wilkins and protoliths. Mylonitic deformation in the lower plate is con- Heidrick, 1982; Wilkinson and others, 1988; Spencer and sidered to be a deeper level expression of, and slightly older others, 1988; Lehman and Spencer, 1989). than, brittle extensional faulting along the detachment fault and its upper plate (Davis, 1983; Spencer and Reynolds, 1986; Howard and John, 1987; Davis and Lister, 1988). Identified Resources Sedimentary and volcanic rock deposition accompanied ex- tension, and these rocks now crop out in the highly faulted Mining and prospecting activity has taken place in upper plate terrane (Davis and others, 1980; Spencer and the Owens and Mesa mineral districts of Spencer and Welty Reynolds, 1989). During the last stages of, or after the end (1989) located in the northeastern and northern parts of the of, the extensional deformation, high-angle faults cut the Swansea Wilderness Study Area (fig. 2). Minor production detachment terrane. Extensional deformation was followed of silver, gold, copper, lead, zinc, and manganese is re- by basaltic and locally silicic volcanism in the middle and corded from these districts. The Swansea mineral district is late Miocene (Suneson and Lucchitta, 1983). These volcan- immediately south and southwest of the study area and the ic rocks are interbedded with locally derived sedimentary Planet mineral district is west of the study area. Significant rocks that filled depressions within the extended terrane. amounts of copper, silver, and minor gold have been pro- The extensional fault system, associated syntectonic duced from these districts (Spencer and Welty, 1989, p. 1 1 4 00 113'45' Castcnecia Hills / Xs,p' 410 _ APPROXIMATE BOUNDARY A \ Artillery mineral OF SWANSEA disuic t ,r To Lake WILDERNESS STUDY AREA / Havasu City (AZ-050-015A) N '4/104, N N Mesa -........; irieral district / Loa;ilavasu ..-- A/00„._ _. , \ / -- Iv ri 95 \ /. Cleopatra \ ANS Bill I Owensnmerai j\ j.\ mineral district \ Alamo To Parker WIC Reservoir Planet Ranch ) 34* R iv district I N, .— 15' yt Planet mint 1 --.-- / 1 Black Burro \ A mineral district --- Plant 1 Mineral Hill \ mineral Alamo Darn mine / district I -.. true. _ • '0 / --- *-• I \ \\ \ A-Sic1/4 I / /-- -- — — /A/ larno X\ \ \ mineral ss_.../ \ N .