Geology topics
Publications and source records attributed to J. C. Wynn.
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This CD-ROM contains vector-based digital maps of the geology and resource assessment of the Venezuela Guayana Shield originally published as paper maps in 1993 in U. S. Geological Survey Bulletin 2062, at a scale of 1:1 million and revised in 1993-95 as separate maps at a scale of 1:500,000. Although the maps on this disc can be displayed at different scales, they are not intended to be used at any scale more detailed than 1:500,000.
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Evaluation of potential high-level nuclear waste repository sites is an area where geophysical capabilities and limitations may significantly impact a major governmental program. Since there is concern that extensive exploratory drilling might degrade most potential disposal sites, geophysical methods become crucial as the only nondestructive means to examine large volumes of rock in three dimensions. Characterization of potential sites requires geophysicists to alter their usual mode of thinking: no longer are anomalies being sought, as in mineral exploration, but rather their absence. Thus the size of features that might go undetected by a particular method take on new significance. Legal and regulatory considerations that stem from this different outlook, most notably the requirements of quality assurance (necessary for any data used in support of a repository license application), are forcing changes in the manner in which geophysicists collect and document their data. -Authors
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This report presents hydrologic data used in the Southern Sand Hills hydrogeology study, which encompasses an area of approximately 4,330 square miles in west-central Nebraska. These data include summary logs of 64 test holes drilled in or adjacent to the study area. Water level data for 240 wells are included. These wells were measured in spring and fall of 1982 and spring of 1983. Water quality samples were collected from 62 irrigation wells. Water quality data include analyses for 18 routine constituents on samples from all wells and analyses for 8 trace constituents on samples from 25 wells. Rainfall data were collected at 30 sites by local observers from April 1982 to October 1983. Surface water data for 103 stream sites in the study area are included. Water discharge was measured at these sites as part of seepage surveys conducted from 1978 to 1982 to determine where and how much streams were gaining or losing water. (USGS)
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Very low frequency electromagnetic, magnetic, and induced polarization methods. The very low frequency electromagnetic resistivity data show high resistivity zones that correlate with siliceous units known to host the gold. The magnetic data clearly identify the mafic and ultramafic dikes which cut metasediments and also fill faults that offset them. The induced polarization method allows examination of the mineralized metasediments in two dimensions by giving vertical sections of resistivity and percent frequency effect, parameters which correlate with silica and pyrite content, respectively. Lithologic units as well as ore zones can thus be mapped in this terrain which is deeply weathered and partially covered by coastal plain sediments.
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No abstract available.
No abstract available.
No abstract available.
Reconnaissance geologic and geochemical sampling was made during the 1978 field season at most of the 50 or so electromagnetic anomalies detected in the 1977 airborne electromagnetic (AEM) survey of the Wadi Bidah district. These Phase 1 studies also included reconnaissance geophysical traverses of nine of the AEM conductors. In addition the AEM anomalies were classified on the basis of this reconnaissance work into a list of priority targets for use in economic studies, and six AEM anomalies were selected for further studies. During Phase 2 conducted in the 1979 field season, ground geophysical work consisting of electromagnetic (EM), self-potential (SP), and selected magnetic surveys were carried out in the six targets selected in the Phase 1 studies. These target areas in aggregate cover about 30 km 2, and are approximately half of the Wadi Bidah Class 1 and Class 2 priority targets found during the 1977 airborne electromagnetic (AEM) survey of parts of the Arabian Shield. The results indicate possible extension of known reserves at the Rabathan area (AEM anomaly B-29), with possible potential for mineralization in the area extending 15-20 km north (anomaly B-13), where the geologic and geophysical environment is similar. An important observation is that mineralization in the B-29 (Rabathan) zone is coincident with narrow SP anomalies superimposed on the larger, broader, and more formational-type SP anomalies encountered in both areas B-29 and B-13. AEM anomaly B-25-26 areahas geophysical characteristics that show in the groundwork and that make it an attractive drill target. EM and SP anomalies are associated, in part, with magnetic anomalies and with exposures of significant limonitic gossan. Wadi al Khadra prospect, not included in the 1977 AEM survey, and the AEM anomaly B-25-26 area were also high-mineralization-potential products of the Phase 2 studies. Target area B-35 remains an unknown quantity, and AEM anomaly B-24 is almost certainly due to a carbonaceous schist. Geochemical results, along with detailed geologic mapping and the geophysical data, indicate several potential mineralized targets. Further detailed geophysics (EM and SP) will assist in understanding the geophysical data thus far collected. Further ground follow-up studies are recommended.