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At least 793 records · Page 44Linked to original sources
USGS2013

Coastal processes influencing water quality at Great Lakes beaches

In a series of studies along the Great Lakes, U.S. Geological Survey scientists are examining the physical processes that influence concentrations of fecal indicator bacteria and related pathogens at recreational beaches. These studies aim to estimate human health risk, improve management strategies, and understand the fate and transport of microbes in the nearshore area. It was determined that embayed beaches act as traps, accumulating Escherichia coli (E. coli) and other bacteria in the basin and even in beach sand. Further, shear stress and wave run-up could resuspend accumulated bacteria, leading to water-contamination events. These findings are being used to target beach design and circulation projects. In previous research, it was determined that E. coli followed a diurnal pattern, with concentrations decreasing throughout the day, largely owing to solar inactivation, but rebounding overnight. Studies at a Chicago beach identified the impact of wave-induced mass transport on this phenomenon, a finding that will extend our understanding of bacterial fate in the natural environment. In another series of studies, scientists examined the impact of river outfalls on bacteria concentrations, using mechanistic and empirical modeling. Through these studies, the models can indicate range and extent of impact, given E. coli concentration in the source water. These findings have been extended to extended lengths of coastlines and have been applied in beach management using empirical predictive modeling. Together, these studies are helping scientists identify and eliminate threats to human and coastal health.

Great Lakes Beaches↗
USGS2015

NEXRAD quantitative precipitation estimates, data acquisition, and processing for the DuPage County, Illinois, streamflow-simulation modeling system

Next-Generation Radar (NEXRAD) has become an integral component in the estimation of precipitation (Kitzmiller and others, 2013). The high spatial and temporal resolution of NEXRAD has revolutionized the ability to estimate precipitation across vast regions, which is especially beneficial in areas without a dense rain-gage network. With the improved precipitation estimates, hydrologic models can produce reliable streamflow forecasts for areas across the United States. NEXRAD data from the National Weather Service (NWS) has been an invaluable tool used by the U.S. Geological Survey (USGS) for numerous projects and studies; NEXRAD data processing techniques similar to those discussed in this Fact Sheet have been developed within the USGS, including the NWS Quantitative Precipitation Estimates archive developed by Blodgett (2013).

Illinois↗
USGS2025

Fiber-optic distributed temperature sensing of hydrologic processes—Diverse deployments and new applications by the U.S. Geological Survey

Fiber-optic distributed temperature sensing instruments harness the temperature-dependent properties of glass to measure temperature continuously along optical fibers by using precise pulses of laser light. In the mid-2000s, this technology was refined for environmental monitoring purposes such as snowpack-air exchange, groundwater/surface-water exchange, and lake-water stratification. Fiber-optic distributed temperature sensing has revealed unprecedented details about preferential flow processes; however, the method is labor intensive and requires specific training, resulting in limited use by the broader water community. With the ongoing national implementation of the U.S. Geological Survey Next Generation Water Observing System, there has been renewed interest in harnessing the unique spatiotemporal monitoring capabilities of fiber-optic distributed temperature sensing. This fact sheet briefly describes this technology, highlights uses by the U.S. Geological Survey, and discusses current applications and future opportunities.

Fact Sheet↗
USGS2000

Publications of the Western Earth Surface Processes Team, 1999

The Western Earth Surfaces Processes Team (WESPT) of the U.S. Geological Survey, Geologic Division (USGS, GD), conducts geologic mapping and related topical earth- science studies in the western United States. This work is focused on areas where modern geologic maps and associated earth-science data are needed to address key societal and environmental issues such as ground-water quality, potential geologic hazards, and land-use decisions. Areas of primary emphasis currently include southern California, the San Francisco Bay region, and the Pacific Northwest. The team has its headquarters in Menlo Park, California, and maintains field offices at several other locations in the western United States. The results of research conducted by the WESPT are released to the public as a variety of databases, maps, text reports, and abstracts, both through the internal publication system of the USGS and in diverse external publications such as scientific journals and books. This report lists publications of the WESPT released in 1999 as well as additional 1997 and 1998 publications that were not included in the previous list (USGS Open-file Report 99-302). Most of the publications listed were authored or coauthored by WESPT staff. The list also includes some publications authored by non-USGS cooperators with the WESPT, as well as some authored by USGS staff outside the WESPT in cooperation with WESPT projects.

Open-File Report↗
USGS2001

Publications of the Western Earth Surface Processes Team 2000

The Western Earth Surface Processes Team (WESP) of the U.S. Geological Survey (USGS) conducts geologic mapping and related topical earth science studies in the western United States. This work is focused on areas where modern geologic maps and associated earth-science data are needed to address key societal and environmental issues such as ground-water quality, potential geologic hazards, and land-use decisions. Areas of primary emphasis in 2000 included southern California, the San Francisco Bay region, the Pacific Northwest, the Las Vegas urban corridor, and selected National Park lands. The team has its headquarters in Menlo Park, California, and maintains smaller field offices at several other locations in the western United States. The results of research conducted by the WESPT are released to the public as a variety of databases, maps, text reports, and abstracts, both through the internal publication system of the USGS and in diverse external publications such as scientific journals and books. This report lists publications of the WESPT released in 2000 as well as additional 1999 publications that were not included in the previous list (USGS Open-file Report 00-215). Most of the publications listed were authored or coauthored by WESPT staff. The list also includes some publications authored by non-USGS cooperators with the WESPT, as well as some authored by USGS staff outside the WESPT in cooperation with WESPT projects. Several of the publications listed are available on the World Wide Web; for these, URL addresses are provided. Many of these Web publications are USGS open-file reports that contain large digital databases of geologic map and related information.

Open-File Report↗
USGS2001

Sand resources, regional geology, and coastal processes for the restoration of the Barataria Barrier shoreline

Louisiana's barrier shorelines are rapidly eroding due to high rates of relative subsidence combined with sea-level rise, repeated storm impacts, and a diminishing sand supply. Due to these factors Louisiana's barrier shorelines are the fastest eroding shorelines in the Nation. In places, the erosion of barrier islands exceeds 65 ft/yr (20 m/yr). One of the best methods for protecting Louisiana’s coastal resources from encroachment from the sea is shoreline restoration using coastal and nearshore sediment sources. The key to restoring barrier shorelines is to find large volumes of high-quality sand and developing cost-effective shallow delivery systems to move these materials. The first major barrier shoreline restoration project proposed by Coast 2050 planners is for the Barataria Basin barrier shoreline that stretches 50 mi (80.5 km) from Belle Pass east to Sandy Point. Many of the barrier shoreline areas in Barataria Basin have become fragmented, low mounds of sand, that are easily washed over by minor storm events, that provide less available habitat than fully developed barrier islands. The objective of this study is to provide information about sand resources, coastal processes, and regional geology which can be collectively used to restore the Barataria Basin barrier shoreline. The focus of this study is the identification of sand resources for the restoration of beaches and creation of backbarrier marshes along this portion of the coast.

Open-File Report↗
USGS2001

Global Positioning System (GPS) survey of Augustine Volcano, Alaska, August 3-8, 2000: data processing, geodetic coordinates and comparison with prior geodetic surveys

Between August 3 and 8,2000,the Alaska Volcano Observatory completed a Global Positioning System (GPS) survey at Augustine Volcano, Alaska. Augustine is a frequently active calcalkaline volcano located in the lower portion of Cook Inlet (fig. 1), with reported eruptions in 1812, 1882, 1909?, 1935, 1964, 1976, and 1986 (Miller et al., 1998). Geodetic measurements using electronic and optical surveying techniques (EDM and theodolite) were begun at Augustine Volcano in 1986. In 1988 and 1989, an island-wide trilateration network comprising 19 benchmarks was completed and measured in its entirety (Power and Iwatsubo, 1998). Partial GPS surveys of the Augustine Island geodetic network were completed in 1992 and 1995; however, neither of these surveys included all marks on the island.Additional GPS measurements of benchmarks A5 and A15 (fig. 2) were made during the summers of 1992, 1993, 1994, and 1996. The goals of the 2000 GPS survey were to:1) re-measure all existing benchmarks on Augustine Island using a homogeneous set of GPS equipment operated in a consistent manner, 2) add measurements at benchmarks on the western shore of Cook Inlet at distances of 15 to 25 km, 3) add measurements at an existing benchmark (BURR) on Augustine Island that was not previously surveyed, and 4) add additional marks in areas of the island thought to be actively deforming. The entire survey resulted in collection of GPS data at a total of 24 sites (fig. 1 and 2). In this report we describe the methods of GPS data collection and processing used at Augustine during the 2000 survey. We use this data to calculate coordinates and elevations for all 24 sites surveyed. Data from the 2000 survey is then compared toelectronic and optical measurements made in 1988 and 1989. This report also contains a general description of all marks surveyed in 2000 and photographs of all new marks established during the 2000 survey (Appendix A).

Alaska↗
USGS2002

Publications of Western Earth Surface Processes Team 2001

The Western Earth Surface Processes Team (WESPT) of the U.S. Geological Survey (USGS) conducts geologic mapping and related topical earth-science studies in the Western United States. This work is focused on areas where modern geologic maps and associated earth-science data are needed to address key societal and environmental issues, such as ground-water quality, landslides and other potential geologic hazards, and land-use decisions. Areas of primary emphasis in 2001 included southern California, the San Francisco Bay region, the Pacific Northwest, and the Las Vegas urban corridor. The team has its headquarters in Menlo Park, California, and maintains smaller field offices at several other locations in the Western United States. The results of research conducted by the WESPT are released to the public as a variety of databases, maps, text reports, and abstracts, both through the internal publication system of the USGS and in diverse external publications such as scientific journals and books. This report lists publications of the WESPT released in 2001, as well as additional 1999 and 2000 publications that were not included in the previous list (USGS Open-File Report 00–215 and USGS Open-File Report 01–198). Most of the publications listed were authored or coauthored by WESPT staff. The list also includes some publications authored by non-USGS cooperators with the WESPT, as well as some authored by USGS staff outside the WESPT in cooperation with WESPT projects. Several of the publications listed are available on the World Wide Web; for these, URL addresses are provided. Many of these web publications are USGS Open-File Reports that contain large digital databases of geologic map and related information.

Open-File Report↗
USGS2002

The Cascadia Subduction Zone and related subduction systems: Seismic structure, intraslab earthquakes and processes, and earthquake hazards

The following report is the principal product of an international workshop titled “Intraslab Earthquakes in the Cascadia Subduction System: Science and Hazards” and was sponsored by the U.S. Geological Survey, the Geological Survey of Canada and the University of Victoria. This meeting was held at the University of Victoria’s Dunsmuir Lodge, Vancouver Island, British Columbia, Canada on September 18–21, 2000 and brought 46 participants from the U.S., Canada, Latin America and Japan. This gathering was organized to bring together active research investigators in the science of subduction and intraslab earthquake hazards. Special emphasis was given to “warm-slab” subduction systems, i.e., those systems involving young oceanic lithosphere subducting at moderate to slow rates, such as the Cascadia system in the U.S. and Canada, and the Nankai system in Japan. All the speakers and poster presenters provided abstracts of their presentations that were a made available in an abstract volume at the workshop. Most of the authors subsequently provided full articles or extended abstracts for this volume on the topics that they discussed at the workshop. Where updated versions were not provided, the original workshop abstracts have been included. By organizing this workshop and assembling this volume, our aim is to provide a global perspective on the science of warm-slab subduction, to thereby advance our understanding of internal slab processes and to use this understanding to improve appraisals of the hazards associated with large intraslab earthquakes in the Cascadia system. These events have been the most frequent and damaging earthquakes in western Washington State over the last century. As if to underscore this fact, just six months after this workshop was held, the magnitude 6.8 Nisqually earthquake occurred on February 28th, 2001 at a depth of about 55 km in the Juan de Fuca slab beneath the southern Puget Sound region of western Washington. The Governor’s Office of the State of Washington estimated damage at more than US$2 billion, making it among the costliest earthquakes in U.S. history.

California, Oregon, Washington↗
USGS2003

Use of boundary fluxes when simulating solute transport with the MODFLOW ground-water transport process

This report describes modifications to a U.S. Geological Survey (USGS) threedimensional solute-transport model (MODFLOWGWT), which is incorporated into the USGS MODFLOW ground-water model as the Ground- Water Transport (GWT) Process. The modifications improve the capability of MODFLOW-GWT to accurately simulate solute transport in simulations that represent a nonzero flux across an aquifer boundary. In such situations, the new Boundary Flux Package (BFLX) will allow the user flexibility to assign the flux to specific cell faces, although that flexibility is limited for certain types of fluxes (such as recharge and evapotranspiration, which can only be assigned to the top face if either is to be represented as a boundary flux). The approach is consistent with that used in the MODPATH model. The application of the BFLX Package was illustrated using a test case in which the Lake Package was active. The results using the BFLX Package showed noticeably higher magnitudes of velocity in the cells adjacent to the lake than previous results without the BFLX Package. Consequently, solute was transported slightly faster through the lake-aquifer system when the BFLX Package is active. However, the overall solute distributions did not differ greatly from simulations made without using the BFLX Package.

Open-File Report↗
USGS2003

Publications of the Western Earth Surface Processes Team 2002

The Western Earth Surface Processes Team (WESPT) of the U.S. Geological Survey (USGS) conducts geologic mapping and related topical earth science studies in the western United States. This work is focused on areas where modern geologic maps and associated earth-science data are needed to address key societal and environmental issues such as ground-water quality, landslides and other potential geologic hazards, and land-use decisions. Areas of primary emphasis in 2001 included southern California, the San Francisco Bay region, the Pacific Northwest, and the Las Vegas urban corridor. The team has its headquarters in Menlo Park, California, and maintains smaller field offices at several other locations in the western United States. The results of research conducted by the WESPT are released to the public as a variety of databases, maps, text reports, and abstracts, both through the internal publication system of the USGS and in diverse external publications such as scientific journals and books. This report lists publications of the WESPT released in 2002 as well as additional 1998 and 2001 publications that were not included in the previous list (USGS Open-File Report 00-215, USGS Open-File Report 01-198, and USGS Open-File Report 02-269). Most of the publications listed were authored or coauthored by WESPT staff. The list also includes some publications authored by non-USGS cooperators with the WESPT, as well as some authored by USGS staff outside the WESPT in cooperation with WESPT projects. Several of the publications listed are available on the World Wide Web; for these, URL addresses are provided. Many of these web publications are USGS open-file reports that contain large digital databases of geologic map and related information. Information on ordering USGS publications can be found on the World Wide Web or by calling 1-888-ASK-USGS. The U.S. Geological Survey’s web server for geologic information in the western United States is located at http://geology.wr.usgs.gov. More information is available about the WESPT is available on-line at the team website.

Open-File Report↗
USGS2004

Submarine ground-water discharge and its role in coastal processes and ecosystems

Submarine ground-water discharge (SGD) has recently been recognized as a phenomenon that can strongly influence coastal water and geochemical budgets and drive ecosystem change. For example, the discharge of nutrient-enriched ground water into coastal waters may contribute significantly to eutrophication and blooms of harmful algae. Similarly, the quantity of SGD can also directly affect the availability of fresh water to coastal communities, impact fragile coastal ecosystems such as estuaries and coral reefs, and influence geomorphology of shoreline features. Moore raised awareness of the global importance of SGD and much effort has been devoted to developing new tracer techniques and methods for the identification and quantification of SGD. Because the discharge of coastal ground water commonly occurs as diffuse seepage rather than focused discharge through identifiable springs, assessing SGD has remained difficult for both oceanographers and hydrologists. Through national and international research programs, Burnett, Moore, Charette, and others have developed a rigorous, systematic approach for quantifying SGD using a wide assortment of tracers and methods. Intercalibration experiments, such as those conducted in coastal waters off Australia, Brazil, and Long Island, NY, demonstrate that careful measurements can accurately quantify SGD, confirm some of the driving mechanisms (e.g. climatic and tidal forcing), and constrain the spatial and temporal scales at which these mechanisms operate. Now that approaches for rigorously quantifying SGD are becoming better established, scientists can now begin to investigate the wide variety of coastal processes affected by SGD.

Open-File Report↗
USGS2009

Questa Baseline and Pre-mining Ground-Water Quality Investigation, 7. A Pictorial Record of Chemical Weathering, Erosional Processes, and Potential Debris-flow Hazards in Scar Areas Developed on Hydrothermally Altered Rocks

Erosional scar areas developed along the lower Red River basin, New Mexico, reveal a complex natural history of mineralizing processes, rapid chemical weathering, and intense physical erosion during periodic outbursts of destructive, storm-induced runoff events. The scar areas are prominent erosional features with craggy headwalls and steep, denuded slopes. The largest scar areas, including, from east to west, Hottentot Creek, Straight Creek, Hansen Creek, Lower Hansen Creek, Sulfur Gulch, and Goat Hill Gulch, head along high east-west trending ridges that form the northern and southern boundaries of the lower Red River basin. Smaller, topographically lower scar areas are developed on ridge noses in the inner Red River valley. Several of the natural scar areas have been modified substantially as a result of large-scale open-pit and underground mining at the Questa Mine; for example, much of the Sulfur Gulch scar was removed by open pit mining, and several scars are now partially or completely covered by mine waste dumps.

Open-File Report↗
USGS2007

Modeling environmental bias and computing velocity field from data of Terra Nova Bay GPS network in Antarctica by means of a quasi-observation processing approach

A semi-permanent GPS network of about 30 vertices has been installed at Terra Nova Bay (TNB) near Ross Sea in Antarctica. A permanent GPS station TNB1 based on an Ashtech Z-XII dual frequency P-code GPS receiver with ASH700936D_M Choke Ring Antenna has been mounted on a reinforced concrete pillar built on bedrock since October 1998 and has recorded continuously up to the present. The semi-permanent network has been routinely surveyed every summer using high quality dual frequency GPS receivers with 24 hour sessions at 15 sec rate; data, metadata and solutions will be available to the scientific community at (http://www.geodant.unimore.it). We present the results of a distributed session approach applied to processing GPS data of the TNB GPS network, and based on Gamit/Globk 10.2-3 GPS analysis software. The results are in good agreement with other authors' computations and with many of the theoretical models.

Open-File Report↗
USGS2008

Carpinteria Coastal Processes Study, 2005-2007: Final report

The United States Geological Survey (USGS), in collaboration with the University of California, Santa Cruz (UCSC), conducted a two-year study of the beach and nearshore coastal processes for the City of Carpinteria and adjacent beaches. The work was performed in response to and worked directly with the United States Army Corps of Engineers (USACE) Project Management Plan (PMP) for the City of Carpinteria: * Carpinteria Shoreline, Santa Barbara County, California PMP (June 2003) www.spl.usace.army.mil/cms/index.php?option=com_content&task=view&id=487&Itemid=31 The City of Carpinteria has experienced significant erosion and storm damage over the last decade (Figure 1.1). A USACE reconnaissance survey has shown shoreline retreat rates that approach 2 m/yr in some locations. The goals of this project are to analyze historical trends/changes in the beach and nearshore environment, document local wave and tidal currents, and assess current beach and nearshore conditions in terms of grain size, beach size and shape, seasonal changes, and nearshore bathymetry. In summary, this work serves to quantify sediment sources, transport and sinks throughout the study area to support USACE and the City of Carpinteria coastal management activities.

California↗
USGS2009

Coastal Processes Study of Santa Barbara and Ventura Counties, California

The Santa Barbara littoral cell (SBLC) is a complex coastal system with significant management challenges. The coastline ranges broadly in exposure to wave energy, fluvial inputs, hard structures, and urbanization. Geologic influence (structural control) on coastline orientation exerts an important control on local beach behavior, with anthropogenic alterations and the episodic nature of sediment supply and transport also playing important roles. Short- and long-term temporal analyses of shoreline change, beach width, and volume change show no obvious trends in regional beach behavior. Extensive armoring along the SBLC has accreted the back beach, narrowing beach widths and in some cases increasing sediment transport. Unarmored beaches have exhibited mild erosion while maintaining similar widths. Harbor constructions have had notable impacts on downdrift beaches, but once the coastal system has equilibrated the signal becomes strongly dampened and littoral-drift gradients driven by natural shoreline orientation again become dominant. Sediment inputs from the Santa Clara River dominate sediment processes on beaches to the south. The SBLC is dominated by episodic flood and storm-wave events. Exceptionally large accretion signals along this stretch of coastline are closely tied to major flood events when large amounts of sediment are deposited in deltas. These deltas decay over time, supplying downdrift beaches with sediment. Storm-wave impacts and gradients in alongshore transport can lead to beach rotations and migrating erosion hotspots when geological controls are weak. Annual and seasonal rates of cross-shore and alongshore transport are at least 2-3 times higher for the more west- and southwest-facing beaches south of the Ventura River as compared to the more sheltered beaches to the west/north. Gross littoral transports are good approximations of net littoral transports for beaches west/north of Ventura as transport is almost purely unidirectional. However, significant transport reversals occur intermittently in the east/south, especially adjacent to the Ventura and Channel Islands Harbors. For this reason, and due to the episodic nature of flood and storm wave events, using dredging rates from the harbors at Ventura and Channel Islands as a proxy for drift rates may be invalid. An extensive grain-size investigation of the surface and shallow subsurface in the nearshore region of the SBLC identified only two sites for potential beach-nourishment material: offshore of Santa Barbara Harbor and Oil Piers. However, seismic-reflection lines offshore of Santa Barbara suggest shallow bedrock (< 1 m), so the volume of coarse material in this area may be limited. Sampling of the Santa Clara River delta was minimal, but this site could be promising. Numerical modeling shows that local beach behavior is primarily influenced by local littoral-drift gradients, which are in turn controlled by natural shoreline orientation. Given the high rates of net littoral drift and the relatively insignificant cross-shore transport in the SBLC, the SBLC should be considered a sediment-limited system (as opposed to a transport-limited system). Management actions, such as any future beach nourishment, would likely have a severely limited life span without employing additional measures that adequately address local littoral-drift gradients to retain added sand.

Open-File Report↗
USGS2009

Proceedings of the XIIIth IAGA Workshop on Geomagnetic Observatory Instruments, Data Acquisition, and Processing

The thirteenth biennial International Association of Geomagnetism and Aeronomy (IAGA) Workshop on Geomagnetic Observatory Instruments, Data Acquisition and Processing was held in the United States for the first time on June 9-18, 2008. Hosted by the U.S. Geological Survey's (USGS) Geomagnetism Program, the workshop's measurement session was held at the Boulder Observatory and the scientific session was held on the campus of the Colorado School of Mines in Golden, Colorado. More than 100 participants came from 36 countries and 6 continents. Preparation for the workshop began when the USGS Geomagnetism Program agreed, at the close of the twelfth workshop in Belsk Poland in 2006, to host the next workshop. Working under the leadership of Alan Berarducci, who served as the chairman of the local organizing committee, and Tim White, who served as co-chairman, preparations began in 2007. The Boulder Observatory was extensively renovated and additional observation piers were installed. Meeting space on the Colorado School of Mines campus was arranged, and considerable planning was devoted to managing the many large and small issues that accompany an international meeting. Without the devoted efforts of both Alan and Tim, other Geomagnetism Program staff, and our partners at the Colorado School of Mines, the workshop simply would not have occurred. We express our thanks to Jill McCarthy, the USGS Central Region Geologic Hazards Team Chief Scientist; Carol A. Finn, the Group Leader of the USGS Geomagnetism Program; the USGS International Office; and Melody Francisco of the Office of Special Programs and Continuing Education of the Colorado School of Mines. We also thank the student employees that the Geomagnetism Program has had over the years and leading up to the time of the workshop. For preparation of the proceedings, thanks go to Eddie and Tim. And, finally, we thank our sponsors, the USGS, IAGA, and the Colorado School of Mines.

Open-File Report↗
USGS2010

Volcanogenic uranium deposits: Geology, geochemical processes, and criteria for resource assessment

Felsic volcanic rocks have long been considered a primary source of uranium for many kinds of uranium deposits, but volcanogenic uranium deposits themselves have generally not been important resources. Until the past few years, resource summaries for the United States or the world generally include volcanogenic in the broad category of "other deposits" because they comprised less than 0.5 percent of past production or estimated resources. Exploration in the United States from the 1940s through 1982 discovered hundreds of prospects in volcanic rocks, of which fewer than 20 had some recorded production. Intensive exploration in the late 1970s found some large deposits, but low grades (less than about 0.10 percent U 3 O 8 ) discouraged economic development. A few deposits in the world, drilled in the 1980s and 1990s, are now known to contain large resources (>20,000 tonnes U 3 O 8 ). However, research on ore-forming processes and exploration for volcanogenic deposits has lagged behind other kinds of uranium deposits and has not utilized advances in understanding of geology, geochemistry, and paleohydrology of ore deposits in general and epithermal deposits in particular. This review outlines new ways to explore and assess for volcanogenic deposits, using new concepts of convection, fluid mixing, and high heat flow to mobilize uranium from volcanic source rocks and form deposits that are postulated to be large. Much can also be learned from studies of epithermal metal deposits, such as the important roles of extensional tectonics, bimodal volcanism, and fracture-flow systems related to resurgent calderas. Regional resource assessment is helped by genetic concepts, but hampered by limited information on frontier areas and undiscovered districts. Diagnostic data used to define ore deposit genesis, such as stable isotopic data, are rarely available for frontier areas. A volcanic environment classification, with three classes (proximal, distal, and pre-volcanic structures), permits use of geologic features on 1:500,000 to 1:100,000 scale maps. Geochemical databases for volcanic rocks are postulated to be more effective than databases for stream sediments or surface radioactivity, both of which tend to be inconsistent because of variable leaching of uranium from soils. Based on empirical associations, spatial associations with areas of wet paleoclimate, adjacent oil and gas fields, or evaporite beds are deemed positive. Most difficult to estimate is the location of depositional traps and reduction zones, in part because they are mere points at regional scale. Grade and tonnage data are reviewed and discussed for 32 deposits in the world. Experience of mining engineers and geologists in Asia suggests that tonnages could be higher than presently known in the Western Hemisphere. Geological analysis, and new data from Asia, suggest a typical or median deposit tonnage of about 5,000 tonnes U 3 O 8 , and an optimistic forecast of discoveries in the range of 5,000 to 20,000 tonnes U 3 O 8 . The likely grade of undiscovered deposits could be about 0.15 percent U 3 O 8 , based on both western and eastern examples. Volcanic terrane is under-explored, relative to other kinds of uranium deposits, and is considered a favorable frontier area for new discoveries.

Open-File Report↗