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At least 91 records · Page 5Linked to original sources
USGS2008

Advancing process‐based watershed hydrological research using near‐surface geophysics: A vision for, and review of, electrical and magnetic geophysical methods

We want to develop a dialogue between geophysicists and hydrologists interested in synergistically advancing process based watershed research. We identify recent advances in geophysical instrumentation, and provide a vision for the use of electrical and magnetic geophysical instrumentation in watershed scale hydrology. The focus of the paper is to identify instrumentation that could significantly advance this vision for geophysics and hydrology during the next 3–5 years. We acknowledge that this is one of a number of possible ways forward and seek only to offer a relatively narrow and achievable vision. The vision focuses on the measurement of geological structure and identification of flow paths using electrical and magnetic methods. The paper identifies instruments, provides examples of their use, and describes how synergy between measurement and modelling could be achieved. Of specific interest are the airborne systems that can cover large areas and are appropriate for watershed studies. Although airborne geophysics has been around for some time, only in the last few years have systems designed exclusively for hydrological applications begun to emerge. These systems, such as airborne electromagnetic (EM) and transient electromagnetic (TEM), could revolutionize hydrogeological interpretations. Our vision centers on developing nested and cross scale electrical and magnetic measurements that can be used to construct a three‐dimensional (3D) electrical or magnetic model of the subsurface in watersheds. The methodological framework assumes a ‘top down’ approach using airborne methods to identify the large scale, dominant architecture of the subsurface. We recognize that the integration of geophysical measurement methods, and data, into watershed process characterization and modelling can only be achieved through dialogue. Especially, through the development of partnerships between geophysicists and hydrologists, partnerships that explore how the application of geophysics can answer critical hydrological science questions, and conversely provide an understanding of the limitations of geophysical measurements and interpretation.

Hydrological Processes↗
USGS2000

Regional Crustal Structures and Their Relationship to the Distribution of Ore Deposits in the Western United States, Based on Magnetic and Gravity Data

Upgraded gravity and magnetic databases and associated filtered-anomaly maps of western United States define regional crustal fractures or faults that may have guided the emplacement of plutonic rocks and large metallic ore deposits. Fractures, igneous intrusions, and hydrothermal circulation tend to be localized along boundaries of crustal blocks, with geophysical expressions that are enhanced here by wavelength filtering. In particular, we explore the utility of regional gravity and magnetic data to aid in understanding the distribution of large Mesozoic and Cenozoic ore deposits, primarily epithermal and porphyry precious and base metal deposits and sediment-hosted gold deposits in the western United States cordillera. On the broadest scale, most ore deposits lie within areas characterized by low magnetic properties. The Mesozoic Mother Lodge gold belt displays characteristic geophysical signatures (regional gravity high, regional low-to-moderate background magnetic field anomaly, and long curvilinear magnetic highs) that might serve as an exploration guide. Geophysical lineaments characterize the Idaho-Montana porphyry belt and the La Caridad-Mineral Park belt (from northern Mexico to western Arizona) and thus indicate a deep-seated control for these mineral belts. Large metal accumulations represented by the giant Bingham porphyry copper and the Butte polymetallic vein and porphyry copper systems lie at intersections of several geophysical lineaments. At a more local scale, geophysical data define deep-rooted faults and magmatic zones that correspond to patterns of epithermal precious metal deposits in western and northern Nevada. Of particular interest is an interpreted dense crustal block with a shape that resembles the elliptical deposit pattern partly formed by the Carlin trend and the Battle Mountain-Eureka mineral belt. We support previous studies, which on a local scale, conclude that structural elements work together to localize mineral deposits within regional zones or belts. This study of mineral deposits of the western United States demonstrates the ability of magnetic and gravity data to elucidate the regional geologic framework or structural setting and to contribute in locating favorable environments for hydrothermal mineralization.

Economic Geology↗
USGS2016

Magnetic and gravity gradiometry framework for Mesoproterozoic iron oxide-apatite and iron oxide-copper-gold deposits, southeast Missouri, USA

High-resolution airborne magnetic and gravity gradiometry data provide the geophysical framework for evaluating the exploration potential of hidden iron oxide deposits in Mesoproterozoic basement rocks of southeast Missouri. The data are used to calculate mineral prospectivity for iron oxide-apatite (IOA) ± rare earth element (REE) and iron oxide-copper-gold (IOCG) deposits. Results delineate the geophysical footprints of all known iron oxide deposits and reveal several previously unrecognized prospective areas. The airborne data are also inverted to three-dimensional density and magnetic susceptibility models over four concealed deposits at Pea Ridge (IOA ± REE), Boss (IOCG), Kratz Spring (IOA), and Bourbon (IOCG). The Pea Ridge susceptibility model shows a magnetic source that is vertically extensive and traceable to a depth of greater than 2 km. A smaller density source, located within the shallow Precambrian basement, is partly coincident with the magnetic source at Pea Ridge. In contrast, the Boss models show a large (625-m-wide), vertically extensive, and coincident dense and magnetic stock with shallower adjacent lobes that extend more than 2,600 m across the shallow Precambrian paleosurface. The Kratz Spring deposit appears to be a smaller volume of iron oxides and is characterized by lower density and less magnetic rock compared to the other iron deposits. A prospective area identified south of the Kratz Spring deposit shows the largest volume of coincident dense and nonmagnetic rock in the subsurface, and is interpreted as prospective for a hematite-dominant lithology that extends from the top of the Precambrian to depths exceeding 2 km. The Bourbon deposit displays a large bowl-shaped volume of coincident high density and high-magnetic susceptibility rock, and a geometry that suggests the iron mineralization is vertically restricted to the upper parts of the Precambrian basement. In order to underpin the evaluation of the prospectivity and three-dimensional models, an extensive statistical summary of density and apparent magnetic susceptibility measurements is presented that includes data on several hundred samples taken from the deposits, altered wall rocks, and unaltered country rocks.

Missouri↗
USGS2016

Forward modeling of gravity data using geostatistically generated subsurface density variations

Using geostatistical models of density variations in the subsurface, constrained by geologic data, forward models of gravity anomalies can be generated by discretizing the subsurface and calculating the cumulative effect of each cell (pixel). The results of such stochastically generated forward gravity anomalies can be compared with the observed gravity anomalies to find density models that match the observed data. These models have an advantage over forward gravity anomalies generated using polygonal bodies of homogeneous density because generating numerous realizations explores a larger region of the solution space. The stochastic modeling can be thought of as dividing the forward model into two components: that due to the shape of each geologic unit and that due to the heterogeneous distribution of density within each geologic unit. The modeling demonstrates that the internally heterogeneous distribution of density within each geologic unit can contribute significantly to the resulting calculated forward gravity anomaly. Furthermore, the stochastic models match observed statistical properties of geologic units, the solution space is more broadly explored by producing a suite of successful models, and the likelihood of a particular conceptual geologic model can be compared. The Vaca Fault near Travis Air Force Base, California, can be successfully modeled as a normal or strike-slip fault, with the normal fault model being slightly more probable. It can also be modeled as a reverse fault, although this structural geologic configuration is highly unlikely given the realizations we explored.

Geophysics↗
USGS1982

Atlantic continental margin of the United States

The objective of this Decade of North American Geology (D-NAG) volume will be to focus on the Mesozoic and Cenozoic evolution of the U.S. Atlantic continental margin, including the onshore coastal plain, related onshore Triassic-Jurassic rift grabens, and the offshore basins and platforms. Following multiple compressional tectonic episodes between Africa and North America during the Paleozoic Era that formed the Appalachian Mountains, the Mesozoic and Cenozoic Eras were dominated by tensional tectonic processes that separated Africa and North America. Extensional rifting during Triassic and Early Jurassic times resulted in numerous tensional grabens both onshore and offshore, which filled with nonmarine continental red beds, lacustrine deposits, and volcanic flows and debris. The final stage of this breakup between Africa and North America occurred beneath the present outer continental shelf and continental slope during Early or Middle Jurassic time when sea-floor spreading began to form new oceanic crust and lithosophere between the two continents as they drifted apart. Postrift subsidence of the marginal basins continued in response to cooling of the lithosphere and sedimentary loading. Geophysical surveys and oil-exploration drilling along the U.S. Atlantic continental margin during the past 5 years are beginning to answer many questions concerning its deep structure and stratigraphy and how it evolved during the rifting and early sea-floor-spreading stages of the separation of this region from Africa. Earlier geophysical studies of the U.S. continental margin used marine refraction and submarine gravity measurements. Single-channel seismic-reflection, marine magnetic, aeromagnetic, and continuous gravity measurements became available during the 1960s.

DNAG Special Publication↗
USGS2007

Geophysical Methods for Investigating Ground-Water Recharge

While numerical modeling has revolutionized our understanding of basin-scale hydrologic processes, such models rely almost exclusively on traditional measurements?rainfall, streamflow, and water-table elevations?for calibration and testing. Model calibration provides initial estimates of ground-water recharge. Calibrated models are important yet crude tools for addressing questions about the spatial and temporal distribution of recharge. An inverse approach to recharge estimation is taken of necessity, due to inherent difficulties in making direct measurements of flow across the water table. Difficulties arise because recharging fluxes are typically small, even in humid regions, and because the location of the water table changes with time. Deep water tables in arid and semiarid regions make recharge monitoring especially difficult. Nevertheless, recharge monitoring must advance in order to improve assessments of ground-water recharge. Improved characterization of basin-scale recharge is critical for informed water-resources management. Difficulties in directly measuring recharge have prompted many efforts to develop indirect methods. The mass-balance approach of estimating recharge as the residual of generally much larger terms has persisted despite the use of increasing complex and finely gridded large-scale hydrologic models. Geophysical data pertaining to recharge rates, timing, and patterns have the potential to substantially improve modeling efforts by providing information on boundary conditions, by constraining model inputs, by testing simplifying assumptions, and by identifying the spatial and temporal resolutions needed to predict recharge to a specified tolerance in space and in time. Moreover, under certain conditions, geophysical measurements can yield direct estimates of recharge rates or changes in water storage, largely eliminating the need for indirect measures of recharge. This appendix presents an overview of physically based, geophysical methods that are currently available or under development for recharge monitoring. The material is written primarily for hydrogeologists. Uses of geophysical methods for improving recharge monitoring are explored through brief discussions and case studies. The intent is to indicate how geophysical methods can be used effectively in studying recharge processes and quantifying recharge. As such, the material constructs a framework for matching the strengths of individual geophysical methods with the manners in which they can be applied for hydrologic analyses. The appendix is organized in three sections. First, the key hydrologic parameters necessary to determine the rate, timing, and patterns of recharge are identified. Second, the basic operating principals of the relevant geophysical methods are discussed. Methods are grouped by the physical property that they measure directly. Each measured property is related to one or more of the key hydrologic properties for recharge monitoring. Third, the emerging conceptual framework for applying geophysics to recharge monitoring is presented. Examples of the application of selected geophysical methods to recharge monitoring are presented in nine case studies. These studies illustrate hydrogeophysical applications under a wide range of conditions and measurement scales, which vary from tenths of a meter to hundreds of meters. The case studies include practice-proven as well as emerging applications of geophysical methods to recharge monitoring.

Professional Paper↗
USGS2014

Geophysical expression of a buried niobium and rare earth element deposit: the Elk Creek carbonatite, Nebraska, USA

The lower Paleozoic Elk Creek carbonatite is a 6–8-km-diameter intrusive complex buried under 200 m of sedimentary rocks in southeastern Nebraska. It hosts the largest known niobium deposit in the U.S. and a rare earth element (REE) deposit. The carbonatite is composed of several lithologies, the relations of which are poorly understood. Niobium mineralization is most enriched within a magnetite beforsite (MB) unit, and REE oxides are most concentrated in a barite beforsite unit. The carbonatite intrudes Proterozoic country rocks. Efforts to explore the carbonatite have used geophysical data and drilling. A high-resolution airborne gravity gradient and magnetic survey was flown over the carbonatite in 2012. The carbonatite is associated with a roughly annular vertical gravity gradient high and a subdued central low and a central magnetic high surrounded by magnetic field values lower than those over the country rocks. Geophysical, borehole, and physical property data are combined for an interpretation of these signatures. The carbonatite is denser than the country rocks, explaining the gravity gradient high. Most carbonatite lithologies have weaker magnetic susceptibilities than those of the country rocks, explaining why the carbonatite does not produce a magnetic high at its margin. The primary source of the central magnetic high is interpreted to be mafic rocks that are strongly magnetized and are present in large volumes. MB is very dense (mean density 3200 kg/m 3 ) and strongly magnetized (median 0.073 magnetic susceptibility), producing a gravity gradient high and contributing to the aeromagnetic high. Barite beforsite has physical properties similar to most of the carbonatite volume, making it a poor geophysical target. Geophysical anomalies indicate the presence of dense and strongly magnetized rocks at depths below existing boreholes, either a large volume of MB or another unknown lithology.

Nebraska↗
USGS2008

Information fusion in regularized inversion of tomographic pumping tests

In this chapter we investigate a simple approach to incorporating geophysical information into the analysis of tomographic pumping tests for characterization of the hydraulic conductivity (K) field in an aquifer. A number of authors have suggested a tomographic approach to the analysis of hydraulic tests in aquifers - essentially simultaneous analysis of multiple tests or stresses on the flow system - in order to improve the resolution of the estimated parameter fields. However, even with a large amount of hydraulic data in hand, the inverse problem is still plagued by non-uniqueness and ill-conditioning and the parameter space for the inversion needs to be constrained in some sensible fashion in order to obtain plausible estimates of aquifer properties. For seismic and radar tomography problems, the parameter space is often constrained through the application of regularization terms that impose penalties on deviations of the estimated parameters from a prior or background model, with the tradeoff between data fit and model norm explored through systematic analysis of results for different levels of weighting on the regularization terms. In this study we apply systematic regularized inversion to analysis of tomographic pumping tests in an alluvial aquifer, taking advantage of the steady-shape flow regime exhibited in these tests to expedite the inversion process. In addition, we explore the possibility of incorporating geophysical information into the inversion through a regularization term relating the estimated K distribution to ground penetrating radar velocity and attenuation distributions through a smoothing spline model. ?? 2008 Springer-Verlag Berlin Heidelberg.

Studies in Computational Intelligence↗
USGS1967

Results of the second phase of the drought-disaster test-drilling program near Morristown, N.J.

The continued drought in northeastern New Jersey through the summer of 1966 with its attendant water-supply problems resulted in an extension of the drought-disaster test-drilling program originally requested by the Office of Emergency Planning on August 30, 1965. Authorization to continue test drilling was fiven by the Office of Emergency Planning on September 26, 1966, with the stipulation that all field work be complete by January 31, 1977. Contractural costs were paid by the Office of Emergency Planning, whereas personnel costs were shared by the U.S. Geological Survey and the New Jersey Department of Conservation and Economic Development, Division of Water Policy and Supply. The work undertaken in 1965 by the Geological Survey was "...to preform the necessary drilling and testing of wells to identify the extent and nature of a reserve ground-water source in the vicinity of the Passaic River near the northern New Jersey metropolitan area." Results of this first phase were made available in the fall of 1966 in Water Resources Circular 16 of the New Jersey Department of Conservation and Economic Development. Three of the five areas tested (figure 1)--two in Parsippany-Troy Hills Township (areas 2 and 4) and one in East Hanover Township (area 1), Morris County--proved capable of providing an aggregate sustained yield of 7.5 million gallons daily (mgd) from wells constructed in sand and gravel deposits. Because significant supplies of ground water for emergency use were located in the first phase of the exploratory test-drilling program, it was though desirable to extend the originally planned studies so as to obtain maximum practicable information on emergency supplies. During this second phase of the investigation, drilling was conducted in 16 sites in Chatham, Madison, and Florham Park Boroughs and in Hanover and East Hanover Townships, Morris County. (See figure 2.) The drilling in Hanover and East Hanover Townships, and part of the drilling done in Florham Park was to explore the availability of large undeveloped ground-water supplies. Drilling in Chatham, Madison, and Florham Park Boroughs was done primarily to determine the extent and continuity of buried valley-fill aquifers, so that a full evaluation of the effects of pumpage from other areas on these already heavily pumped areas could be made. In addition, it was anticipated that the drilling could help in defining the feasibility of artificial recharge of the heavily pumped areas and in the determination of the prospective method of recharge and points of emplacement. Arrangements for easements with landowners, preparation of specifications for well drilling and seismic work, and supervision of well drilling and seismic contracts were all performed by the New Jersey District, Water Resources Division of the Geological Survey. Prior to the test drilling, seismic exploration under contract with Alpine Geophysical Associates of Norwood, N. J. was conducted at five locations in the Chatham-Madison-Florham Park area and at one place in Parsippany-Troy Hills Township. The seismic work was done to determine the most favorable location for a test well at several potential test-well sites and to help in the interpretation of subsurface geology between test sites. Contracts for the drilling of the test holes were awarded during November and drilling commences on November 30. Kaye Well drilling, Inc. of Jackson, N. J. was the recipient of a contract for eight of the test holes, and a second contract was awarded to Rinbrand Well Drilling Co., Inc. of Glen Rock, N. J.--also for eight test holes. Acknowledgment is due to the many public officials of Chatham, Madison, Florham Park, Morristown, and East Hanover Township as well as officials of the Braidburn Corporation and Esso Research and Engineering Co., who cooperated by making their lands available for exploration.

New Jersey↗
USGS2025

Near-surface geophysics: Environmental applications

The field of geophysics encompasses a broad and diverse compilation of methodologies that employs principles of physics to characterize properties of earth materials within the subsurface. While geophysical methods have a long history in resource exploration and studies of Earth’s interior, the subdiscipline of “near-surface geophysics” has evolved in recent decades for examination of the shallow, near-surface environment for a range of purposes ranging from archaeological or forensic investigations to assessment of geologic, hydrologic, biologic, and geochemical properties and processes. “Environmental geophysics” are near-surface geophysical studies and methods that focus on understanding natural systems (e.g., watershed hydrology, groundwater–surface water connections, biophysical processes) as well as research pertaining to anthropogenic impacts and land management, (e.g., contamination and remediation, saltwater intrusion, agricultural practices). This field can be further subdivided into subdisciplines focused on specific topics and applications, such as water resources and hydrology (hydrogeophysics) or biologic and microbial processes (biogeophysics). Studies in environmental geophysics span a range of scales, from pore-scale laboratory tests to watershed-scale or regional field experiments. Methods vary by the nature of physics employed, the specific measurement acquired, and how that data is ultimately processed and analyzed to produce interpretable results. There exists further diversity in the acquisition logistics, geometry, and timing of data collection. Geophysical data can be collected in boreholes (one-dimensional, 1-D, vertical profiles), along survey lines (two-dimensional, 2-D, cross-sections), or in dense sensor arrays or gridded profiles (three-dimensional, 3-D, models). Regarding the temporal aspect, studies can conduct one-time geophysical surveys to obtain detailed imaging of subsurface structure or use timelapse and continuous monitoring to investigate variations in subsurface properties over time. The cumulation of all possible permutations of these factors (method, acquisition geometry, survey design, and target application) results in an immense diversity among environmental geophysical studies. Nevertheless, this field remains unified in the pursuit of understanding natural and human-impacted near-surface environments through geophysical investigations. Here we highlight some key references within environmental geophysics. Resources on geophysical theory, acquisition logistics, processing and inversion workflows, and example case studies are categorized into the most common geophysical classes within Geophysical Methods. Lastly, example references for the dominant types of applications in environmental geophysical studies are catalogued in Environmental Applications.

Book chapter↗
USGS1997

Evaluation of bridge-scour data at selected sites in Ohio

Scour data collected during 1989-94 were evaluated to determine whether pier scour and contraction scour occurred at 22 bridge sites in Ohio. Pier-scour depths computed from selected pier-scour prediction equations were compared with measured pier-scour depths, and the accuracy of the prediction equations were evaluated. Observed pier-scour relations were compared to relations developed through laboratory research. Mean streambed elevations were evaluated to determine the depth of contraction scour. Channel stability was assessed by use of mean streambed elevations at the approach section. Ground-penetrating radar was used at all sites to investigate the presence of historical scour. Pier scour was observed in 45 of 47 scour measurements made during floods; 84 cases of pier scour were documented, 83 at solid-wall piers and 1 at a capped-pile type pier. Estimated recurrence intervals for 27 of the 35 measured streamflows, all on unregulated streams, were less than 2 years. Seventeen pier-scour prediction equations were evaluated. The Froehlich Design equation was found to most closely meet the 'best design equation' criteria for all 84 cases of the observed data. The Larras equation was found to be the best design equation for the observed data where approach-flow attack angles were 10 degrees or less. Observed pier-scour depths and flow depths ranged from 0.5 to 6.1 feet and 3.0 to 19.8 feet, respectively. All pier-scour depths were less than 2.4 times the corresponding pier width. Selected factors were normalized by dividing by effective pier width. LOWESS curves were developed using the 84 cases of observed pier scour. Normalized scour depth increased with normalized flow depth; however, the rate of increase appeared to lessen as normalized flow depth exceeded 2.5. Normalized scour depths increased rapidly as flow intensity approached the threshold value of 1 and then decreased as flow intensities exceeded this threshold. Normalized scour depth was found to increase with Froude number, and a steeper slope was evident for Froude numbers exceeding 0.2. Normalized scour depth was found to increase with median grain size up to about 10 millimeters for bed material near the pier, then decrease for median grain sizes greater than 10 millimeters. Normalized scour depth was also found to decrease as sediment gradation of bed material near the pier increased. The observed pier-scour relations determined from the field measurements tend to support conclusions by previous researchers of streambed scour, except for the previous finding that normalized scour depth decreases consistently with increasing median grain size. Possible factors that may have influenced the observed trends in the relation between normalized scour depth and median grain size in this study are cohesion and scour measurements made at nonequilibrium conditions. LOWESS curves were developed for 45 of 84 cases of observed pier scour where approach-flow attack angles were less than or equal to 10 degrees. These curves were visually compared to LOWESS curves developed from all observations of pier scour. For three relations, differences in the trends of the LOWESS curves were of sufficient magnitude to warrant discussion. Contraction scour was observed in 4 of the 47 scour measurements and ranged from 0.8 to2.3 feet in depth. Analysis of annual mean streambed approach-section elevations indicated that approach sections were generally stable at 18 of the 22 sites. Ground-penetrating radar, a geophysical method that enables subsurface exploration of the streambed when conditions are favorable, was used at all sites to determine whether historical scour had occurred. Results of the ground-penetrating radar surveys at 20 sites in 1990 indicated the presence of historical scour surfaces at 5 sites. At four of the five sites showing evidence of possible historical scour, differences between the estimated depth of historical scour and the maximum observed scour were w

Water-Resources Investigations Report↗
USGS1977

Borehole geophysical investigations in the south Texas uranium district

Contrasts of electrical properties between uranium deposits and their host rocks in South Texas are subtle. In places where deposits are small or deep, conventional geophysical well-logging techniques and hole-to-hole measurements may be the only practical method to detect changes in rock properties associated with the occurrence of uranium ore deposits. Two separate ore-producing areas in South Texas were chosen for studying borehole geophysical techniques applied to uranium-exploration problems. Extensive measurements of physical properties were made on cores and taken from holes where electrical-resistivity, induced-polarization and gamam-ray logs were run. These analyses show that: (1) induced-polarization anomalies are caused by a change in pyrite content and clay-sized material content and (2) resistivity anomalies are associated with a change in clay-sized material content and cementation. In addition to conventional borehole techniques, hole-to-hole induced-polarization and resistivity tests were made in South Texas. These measurements were made by placing a current source down one hole and a receiver cable down an adjacent hole whose separation ranged from 30 to 300 m and hole depths varied from 80 to 270 m. These tests show that hole-to-hole measurements can be used to detect changes in physical properties, associated with uranium ore, that occur between boreholes. Hole-to-hole measurements provide a link between surface measurements and well logs and can minimize the amount of drilling needed to locate an ore deposit. Accordingly, borehole geophysics will become an increasingly important evaluation tool as mineral exploration goes deeper.

Texas↗
USGS1990

Metallic-mineral assessment of the Aban Al Ahmar quadrangle, sheet 25F, Kingdom of Saudi Arabia

Comprehensive detailed interdisciplinary study assesses the metallic-mineral-resource potential in the Aban Al Ahmar Quadrangle of the Kingdom of Saudi Arabia, located in the eastern margin of the northeastern Arabian Shield, utilizing techniques of geophysics, geologic mapping, remote sensing and geochemistry. The landscape of the study area is characterized by isolated mountain groups, inselbergs, and local tracts of dissected hills separated by broad, low-relief peneplain. Topics covered include mining and exploration history; geological setting; interpretation of geophysical anomalies; limonitic hydrothermally altered and mineralized rocks; geochemical interpretation; mineral resource potential; skarn deposiits associated with intermediate igneous rocks; gold deposits; tin/tungsten skarn deposits; etc.

Aban Al Ahmar quadrangle↗
USGS1960

The chief oxide-burgin area discoveries, East Tintic district, Utah; A case history

In 1955 exploration for base and precious metals was undertaken by Bear Creek Mining Company immediately north of the Main Tintic district , Utah . During the course of this work Bear Creek became interested in the East Tintic district , primarily as a result of the activities of the U.S. Geological Survey in that area . Data published on the East Tintic district by the Survey and others were studied and map data made available from various mining companies were compiled. Preliminary economic studies were made to determine the present day value of the type of ore body discovered previously in the district . Encouraging results from these investigations led to the selection of specific targets for exploration. Recommendations for a project program were made and approved. Negotiations were successfully concluded in mid-1956 for a unit lease agreement on lands in the East Tintic district owned by the Tintic Standard and Chief Consolidated mining companies and their subsidiaries. Of the targets selected for exploration, the Chief Oxide area seemed to be one of the most prominent. Our preliminary work in the Chief Oxide area corroborated the findings of the U.S. Geological Survey described in Part I of this paper. After careful consideration it was decided to gamble the cost of an exploration shaft in this area for the purpose of providing an underground drilling platform. We also hoped by means of underground workings to establish the existence and nature of the postulated fault. A limited amount of surface drilling was done prior to shaft sinking in order to locate a shaft site and also to obtain additional information of subvolcanic structure and alteration. Underground exploration in the Chief Oxide area was started in January, 1957. The Burgin shaft was sunk to a depth of 1,100 feet and by August, 1959, lateral development on the 1050 level totaled 4,721 feet and underground diamond drilling totaled 15,480 feet. Results of the work done to date are as follows: ( a ) Identification of the sedimentary rock section and an interpretation of the structure in the Burgin mine area . (b) Discovery by penetration of the previously postulated East Tintic thrust fault. (c) Discovery of large zones of manganese oxides and carbonates, which were found to be closely related to silver-lead-zinc mineralization. (d) Discovery of ore-grade lead-zinc mineralization within the footwall rocks of the East Tintic thrust. (e) Discovery of high-grade silver-lead ore within the thrust zone. Insofar as ore localization is concerned the most important structural feature in the Burgin mine area is the East Tintic thrust fault- a fact that opens up new ore potential over a large part of the East Tintic district not previously explored. Although the discoveries to date must be attributed essentially to the application of geology to exploration, the tools of geochemical prospecting and geophysics were also used, and the geochemical work, in particular, was found to be a definite aid in the selection of areas for further exploration.

Utah↗
USGS1978

Applying satellite technology to energy and mineral exploration

IGCP Project 143 ("Remote Sensing and Mineral Exploration"), is a worldwide research project designed to make satellite data an operational geological tool along with the geologic pick, hand lens, topographic map, aerial photo and geophysical instruments and data that comprise the exploration package. While remote sensing data will not replace field exploration and mapping, careful study of such data prior to field work should make the effort more efficient.

Episodes↗
USGS2025

Alteration mapping in granitic gneiss using handheld geophysical and geochemical instruments: Implications for iron oxide-apatite and rare earth elements exploration

The Adirondack Mountains of New York, U.S.A. contain iron oxide-apatite (IOA) mineral deposits with variable concentrations of rare earth elements (REE). The IOA mineral deposits are typically hosted in the Lyon Mountain Granite Gneiss and are spatially correlated with extensive Na metasomatism (albitization) of the surrounding country rocks, although some mineral deposits also occur in metagabbro, paragneiss, and anorthosite hosts. The location of albitization zones is key to finding new IOA mineral deposits and better understanding the mineralization processes associated with their genesis. However, the Na alteration zones are generally not visibly identifiable in outcrop or hand specimens because the color and textural changes are subtle and are thus difficult to map. Here, we discuss the results from testing two spectroscopic techniques (handheld, field gamma-ray spectroscopy, and portable X-ray fluorescence (pXRF)) to characterize albitization zones surrounding IOA mineral deposits. The gamma-ray and pXRF spectrometers successfully distinguished the relative intensity of alteration in the Lyon Mountain Granite Gneiss based on the K abundance. The measured K content decreases towards the IOA mineral deposits, and the magnitude and width of the gradient are similar along the strike of each mineral deposit. Elevated Th and U values are present in host rocks adjacent to REE-bearing IOA mineral deposits. The pXRF and gamma-ray spectrometer K values are remarkably consistent with laboratory-based, whole-rock XRF compositional data and, therefore, useful for semi-quantitative analysis. Notably, albitization aureoles are consistent around REE-rich and REE-poor mineral deposits, suggesting that saline fluids are essential for the petrogenesis of IOA mineral deposits but may not be critical to REE mineralization. Ultimately, this study demonstrates the utility of handheld gamma-ray and pXRF spectrometry for identifying otherwise cryptic albitization gradients associated with IOA mineral deposits in granitic gneiss.

New York↗
USGS1979

Analysis of borehole geophysical information across a uranium deposit in the Jackson Group, Karnes County, Texas

Borehole geophysical studies across a uranium deposit in the Jackson Group, South Texas, show the three geochemical environments often associated with uranium roll-type deposits: an altered (oxidized) zone, an ore zone, and an unaltered (reduced) zone. Mineralogic analysis of the total sulfides contained in the drill core shows only slight changes in the total sulfide content among the three geochemical regimes. However, induced polarization measurements on the core samples indicate that samples obtained from the reduced side of the ore zone are more electrically polarizable than those from the oxidized side of the ore zone, and therefore probably contain more pyrite. Analysis of the clay-size fraction in core samples indicates that montmorillonite is the dominant clay mineral. High resistivity values within the ore zone indicate the presence of calcite cement concentrations that are higher than those seen outside of the ore zone. Between-hole resistivity and induced polarization measurements show the presence of an extensive zone of calcite cement within the ore zone, and electrical polarizable material (such as pyrite) within and on the reduced side of the ore zone. A quantitative analysis of the between-hole resistivity data, using a layered-earth model, and a qualitative analysis of the between-hole induced polarization measurements showed that mineralogic variations among the three geochemical environments were more pronounced than were indicated by the geophysical and geologic well logs. Uranium exploration in the South Texas Coastal Plain area has focused chiefly in three geologic units: the Oakville Sandstone, the Catahoula Tuff, and the Jackson Group. The Oakville Sandstone and the Catahoula Tuff are of Miocene age, and the Jackson Group is of Eocene age (Eargle and others, 1971). Most of the uranium mineralization in these formations is low grade (often less than 0.02 percent U3O8) and occurs in shallow deposits that are found by concentrated exploratory drilling programs. The sporadic occurrence of these deposits makes it desirable to develop borehole geophysical techniques that will help to define the depositional environments of the uranium ore, which is characterized by geochemical changes near the uranium deposits. Geochemical changes are accompanied by changes in the physical characteristics of the rocks that can be detected with borehole geophysical tools. This study is concerned with a uranium deposit within the Jackson Group that is located just east of Karnes City, Tex. Five holes were drilled on this property to obtain borehole geophysical data and cores. The cores were analyzed for mineralogic and electrical properties. The borehole geophysical information at this property included induced polarization, resistivity, gamma-gamma density, neutron-neutron, gamma-ray, caliper, and single-point-resistance logs. Between-hole resistivity and induced polarization measurements were made between hole pairs across the ore deposit and off the ore deposit.

Open-File Report↗
USGS1982

Geology of areas marked by geophysical anomalies (B-35 and B-34), Wadi Bidah District, Kingdom of Saudi Arabia

Geophysical surveys in the Wadi Bidah district, in the southwestern part of the Kingdom of Saudi Arabia, have revealed anomalies of the type that may be caused by deposits of massive sulfides. Accordingly, a study was undertaken to investigate the geologic environment associated with the geophysical anomalies and to determine whether mineral exploration of the anomalous areas might be warranted. An extensive geochemical sampling program did not disclose any evidence of ore mineral concentrations in the rocks. Detailed geologic mapping shows the anomalous areas to be underlain by Precambrian carbonaceous graywacke, the outcrop patterns of which closely fit the anomaly patterns. Field evidence and petrologic studies indicate that carbonaceous material in the rocks is the cause of the geophysical anomalies. Nothing was found in the anomalous areas that suggests the presence of mineral deposits of commercial grade, and further mineral investigations or exploration in the areas is not recommended.

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