Jeff Wynn | United States Geological Survey (original) (raw)

ASTEROID PHYSICS by Jeff Wynn

Lunar & Planetary Science Conference, 2024

On 8 January 2014 US government satellite sensors detected three atmospheric detonations in rapid... more On 8 January 2014 US government
satellite sensors detected three atmospheric detonations
in rapid succession about 84 km north of Manus
Island, outside the territorial waters of Papua New
Guinea (20 km). Analysis of the trajectory suggested
an interstellar origin of the causative object CNEOS
2014-01-08: an arrival velocity relative to Earth more
than ~45 km s−1, and a vector tracked back to outside
the plane of the ecliptic. In 2022 the US Space
Command issued a formal letter to NASA certifying a
99.999% likelihood that the object was interstellar in
origin. Along with this letter, the US Government
released the fireball light curve as measured by
satellites, which showed three flares separated by a
tenth of a second from each other. The bolide broke
apart at an unusually low altitude of ~17 km. The
object was substantially stronger than any of the other
272 objects in the CNEOS catalog, including the ~5%-
fraction of iron meteorites from the solar system.
Calculations of the fireball light energy suggest that
about 500 kg of material was ablated by the fireball
and converted into ablation spherules with a small
efficiency. The fireball path was localized to a 1 km-
wide strip based on the delay in arrival time of the
direct and reflected sound waves to a seismometer
located on Manus Island.

Introduction: Vesicles of various size and shape are often observed in impactite melt glasses fro... more Introduction: Vesicles of various size and shape are often observed in impactite melt glasses from both large and small scale impact structures. Particularly, both the so-called white and black silicate-dominated impact glasses found at the very young (app. 300 years), small scale impact site of an iron-meteorite in the desert sand dunes at Wabar, Saudi Arabia exhibit abundant vesicles [see e.g. 1, Fig. 1.]. It is commonly agreed that vesicles in impactites are the result of simple outgassing from a silicate melt controlled by decreasing solubility during the decompression phase [1]. The gasses dissolving from the silicate melts are assumed to include both water and carbon dioxide. The morphology of the gas vesicles will reflect the gas-melt interface, approximating a sphere and reflecting the overall dynamic of the melt as it cools to its melting temperature. This is in accordance with the observation of essential circular vesicle cross-sections in thin sections of impactites. Furthermore, as simple gasses will not form solids on further cooling to ambient conditions, we may assume that an essentially smooth glass-vesicle interface morphology will be formed and preserved, and this should be observed at all intermediate to high magnifications. Results and discussion: To test this assumption we have investigated glass-vesicle interfaces in black Wabar impactites at various resolutions using tomography and microscopy. As an example of the observed interface structures Figure 1 shows a vesicle exposed by cutting through the impactite.

The Wabar meteorite impact site in central Saudi Arabia, first reported by Henry St. John (Abdull... more The Wabar meteorite impact site in central Saudi Arabia, first reported by Henry St. John (Abdullah) Philby in 1933, is unique in several ways. Despite a > 6,000 year fission-track date, the impact must be very recent according to certain field relationships, a conclusion supported by thermoluminescence dates of less than 250 years. Along with several other small meteoroid impact events that have come to light in the past few decades, the new age-date suggests a reconsideration of the frequency of these types of "city-buster" impacts. The Wabar impact event also took place entirely in sand, permitting a much clearer and simpler reconstruction of the physical processes of a hypervelocity impact. The event sequence, which took place in just a few seconds, generated a unique array of impactite that includes a black glass (90 percent local sand and 10 percent meteorite) and a shock-generated, coarsely laminar bleached-white sandstone. The event took place in one of the most inhospitable areas on Earth, the middle of the Rub' Al-Khali, the largest contiguous sand desert in the world. Here temperatures during one magnetic profile reached 61 o C (142 o F).

In their explorations of the Red Planet, Mars Pathfinder and Mars Global Surveyor have encountere... more In their explorations of the Red Planet, Mars Pathfinder and Mars Global Surveyor have encountered a well-known class of surface features common on the Moon and on Mercury: impact craters. They are very uncommon on the Earth - but they exist. One of the youngest and best-preserved is in the Rub' al-Khali, the Empty Quarter of Saudi Arabia. The difficulty is that this is one of the most inaccessible and formidable deserts on our planet.

Scientific American, Nov 1998

Journal of Geophysical Research, 2004

Journal of Environmental & Engineering Geophysics, Vol. 7, No. 4, p. 143-150., 2002

OCEAN PHYSICS by Jeff Wynn

ArXiv, 2023

We have conducted an extensive towed-magnetic-sled survey during the period 14-28 June, 2023, ove... more We have conducted an extensive towed-magnetic-sled survey during the period 14-28 June, 2023, over the seafloor about 85 km north of Manus Island, Papua New Guinea, and found about 700 spherules of diameter 0.05-1.3 millimeters in our samples, of which 57 were analyzed so far. Approximately 0.26 km 2 of seafloor was sampled in this survey, centered

INDUCED POLARIZATION AND MAGNETIC RESPONSE OF TITANIUM-BEARING PLACER DEPOSITS IN THE SOUTHEASTERN UNITED STATES, 1985

The induced polarization IP response of economically valuable placer deposits of altered ilmenite... more The induced polarization IP response of economically valuable placer deposits of altered ilmenite and other heavy minerals in fossil beach-complex sediments of northeastern Florida is unusually strong. This suggests that mineral-resource exploration and evaluation could be made much more efficient by use of the IP method. Field and laboratory studies conducted on detrital heavy-mineral deposits and on commercial concentrate stockpiles in Florida indicate that of the two main titanium ore minerals, altered ilmenite has a strong IP response while that of rutile is weak.

Induced polarization spectra for altered ilmenite were acquired by a unique laboratory sampling method and are distinctly different from those of pyrite. Placer ilmenite consistently shows a phase-angle maximum at about 10 Hz, whereas pyrite has a phase-angle maximum that varies with grain size but generally centers at around approximately 0.1 Hz. These differences along with the unusually strong amplitude and phase variations observed in the IP response of altered ilmenite, should
permit separation of this altered ilmenite from pyrite in the field under typical northeastern Florida survey conditions. In northern Florida, our experiments suggest that one volume percent of ilmenite corresponds to about 5-6 millivolt-seconds/volt inherent chargeability (or about 6-7 milliradians phase shift at 1.0 Hz). This permits quantification of ilmenite reserves by use of surface IP measurements.

The magnetic susceptibility of altered placer ilmenite concentrates was significant, ranging from 0.0025 to 0.0045 SI units), yet substantially below that reported in the literature for stoichiometric ilmenite. Field magnetic measurements have not been diagnostic of the presence of ilmenite, due in part to the surprisingly low susceptibilities as well as to the low concentrations found in southeastern U.S. economic deposits. High resolution aeromagnetic surveys, however, have been successfully
used regionally in outlining target areas for drilling.

Other geophysical exploration techniques for ilmenite-bearing placers, such as gamma-ray spectrometry and Side-Looking Airborne Radar (SLAR), are dependent on geophysical signatures of associated minerals, and/or geomorphologic associations, and detect only surface characteristics. Consequently quantification of resources with field measurements is not possible with these methods.

The studies carried out so far encourage us to think that IP might be the most efficient means to locate and delineate analogous ilmenite
concentrations in submerged U.S. Continental Shelf sediments. If on-going research proves this to be the case, IP will become a major marine exploration tool in the evaluation and exploration for placer mineral resources within the U.S. Exclusive Economic Zone.

US Geological Survey Open File Report 85-756, 1985

The induced polarization (IP) response of economically valuable placer deposits of altered ilmeni... more The induced polarization (IP) response of economically valuable placer
deposits of altered ilmenite and other heavy minerals in -fossil beach-complex sediments of northeastern Florida is unusually strong. This suggests that mineral-resource exploration and evaluation could be made much more efficient by use of the IP method. Field and laboratory studies conducted on detrital heavy-mineral deposits and on commercial concentrate stockpiles in Florida indicate that of the two main titanium ore minerals, altered ilmenite has a strong IP response while that of rutile is weak.
Induced polarization spectra for altered ilmenite were acquired by a
unique laboratory sampling method and are distinctly different from those of pyrite. Placer ilmenite consistently shows a phase-angle maximum at about 10 Hz, whereas pyrite has a phase-angle maximum that varies with grain size but generally centers at around approximately 0.1 Hz. This differences along with the unusually strong amplitude and phase variations observed in the IP response of altered ilmenite should permit separation of this altered ilmenite from pyrite in the field under typical northeastern Florida survey conditions. In northern.Florida» our experiments suggest that one volume percent of ilmenite corresponds to about 5-6 millivolt-seconds/volt inherent chargeability (or about 6-7 milliradians phase shift at 1.0 Hz). This permits quantification of ilmenite reserves by use of surface IP measurements.
The magnetic susceptibility of altered placer ilmenite concentrates was
significant (ranging -from 0.0025 to 0.0045 SI units), yet substantially below that reported in the literature for stoichiometric ilmenite. Field magnetic measurements have not been diagnostic of the presence of ilmenite due in part to the surprisingly low susceptibilities as well as to the low concentrations found in southeastern U.S. economic deposits. High-resolution aeromagnetic surveys however have been successfully used regionally in outlining target areas for drilling. Other geophysical exploration techniques for ilmenite-bearing placers such as gamma-ray spectrometry and Side-Looking Airborne Radar (SLAR) are dependent on geophysical signatures of associated minerals and/or geomorphologic associations and detect only surface characteristics. Consequently
quantification of resources with field measurements is not possible with
these methods.
The studies carried out so far encourage us to think that IP might be
the most efficient means to locate and delineate analogous ilmenite
concentrations in submerged U.S. Continental Shelf sediments. If on-going research proves, this to be the case IP will become a major marine exploration tool in the evaluation and exploration for placer mineral
resources within the U.S. Exclusive Economic Zone.

A new technology developed by the US Geological Survey now allows for fast, direct detection of h... more A new technology developed by the US Geological Survey now allows for fast, direct detection of hydrocarbon plumes both in rivers and drifting in the deep ocean. Recent experiments show that the method can also detect and quantify hydrocarbons buried in river sediments and estuaries. This approach uses a variant of induced polarization, a surface-sensitive physical property of certain polarizable materials immersed in an electrolyte that can accept and adsorb charge under an inducing voltage. Known polarizable materials include most sulfides, ilmenite (FeTiO3), metallic objects such as buried wrecks and pipelines, and now hydrocarbons. The hydrocarbon-in-water response to induced polarization is in fact nearly two orders of magnitude greater than the IP response of any of the hard minerals. The oil:water detection limit for hydrocarbons so far is down to 0.0002% in the laboratory.

Titanium is abundant in the Earth's crust, but it can be economically extracted from only a limit... more Titanium is abundant in the Earth's crust, but it can be economically extracted from only a limited group of minerals, principally rutile (Ti0 2) and ilmenite (FeTi0 3), both found mainly in fossil beach-complex placer deposits. Both minerals have only a weak magnetic susceptibility, insufficient to permit correlation between magnetic surveys and known titanium-rich deposits. However, ilmenite shows an unusually strong induced-polarization (IP) response, whereas the IP response of rutile is relatively weak. IP spectral signatures for ilmenite acquired in laboratory and field settings are also distinctly different from those of other polarizing materials, for instance pyrite. A nonfloating, towed-streamer IP system was designed and deployed in surveys off the coasts of Virginia and Georgia. When the cable lies on the sea floor, calculations indicate that only about 8 percent of the injected current actually finds its way into the underlying sediment. Partly because of this high transmitted-current to injected-current ratio, a stationary-streamer IP noise envelope of about 2-4 milliradians (mrad) phase shift and a towed-streamer noise envelope of 4-6 mrad were measured. Two surveys were undertaken, one of which covered about 30 traverse km of the Atlantic continental shelf (ACS) and crossed two vibracore sites where geo-logic control could be obtained. Many IP anomalies were observed, with some ranging as high as 20 + mrad; about one-third of the shallow bathymetric lows (probable paleochannels) showed anomalous IP results. Modeling suggests that these anomalies may have been

A system is provided for detecting minerals and metal containing materials which are located in s... more A system is provided for detecting minerals and metal containing materials which are located in sediment deposits on the ocean floor and which exhibit an induced polarization response. A streamer cable, which, in use, is towed in the sea behind a ship, includes a series of transmitters and receivers at the free end thereof. The cable is towed such that the free end is in contact with the sea floor and the transmitters are used to transmit a square wave electrical current into the sediment there. The receivers are used to detect any secondary signals produced by an induced polarization source located on or beneath the sea floor in response to electrical current. Preamplifers connected to the receivers provide noise rejection. On-board electronics process the secondary signals to determine measurement parameters characteristic of the source thereof so as to identify the source. A computer uses this information, together with simultaneously acquired global position data, to determine the location of the source.

A method is provided for detecting minerals and metal containing materials which are located in s... more A method is provided for detecting minerals and metal containing materials which are located in sediment deposits on the sea floor and which exhibit an induced polarization response. In this method, a streamer cable is towed in the sea behind a ship. The cable has transmitters and receivers at the free end thereof and the cable is towed such that its free end is close to or trenches into the sea floor. The transmitters are used to transmit a square wave electrical current into the sediment of the sea floor While the receivers are used detect any secondary signals produced by an induced polarization source located on or in the sea floor in response to the electrical current. The secondary signals are processed to determine measurement parameters characteristic of the source of the secondary signals so as to determine the location of the source.

Since 2001, researchers at the U.S. Geological Survey (USGS) have teamed with industry partners t... more Since 2001, researchers at the U.S. Geological Survey (USGS)
have teamed with industry partners to explore the commercial
applications of the USGS-patented (2001) Marine Induced
Polarization (IP) Streamer system that has the ability to
rapidly map very low percentage mineral and metallic particle
distributions on and beneath the seafloor in three dimensions
and with high resolution.

Comment on “Benefits of the induced polarization geoelectric method to hydrocarbon exploration” (P. Veeken, P. J. Legeydo, Y. A. Davidenko, E. O. Kudryavceva, S. A. Ivanov, and A. Chuyaev, 2009, Geophysics, 74, no. 2, B47– B59)

With the extensive filtering described, the poorly coupled transmitter-receiver dipoles, and the ... more With the extensive filtering described, the poorly coupled transmitter-receiver dipoles, and the EM coupling issue,
it is not clear to us that the anomalies (Veeken et al, 2009) describe are real.

Abstract Raw sewage and industrial waste have been dumped into sensitive estuaries, bays, and sou... more Abstract
Raw sewage and industrial waste have been dumped into sensitive estuaries, bays, and sounds for centuries. The full extents of the resulting sludge deposits are largely unknown, because they move
in response to tidal and long-shore currents, and because they are often buried by younger inert sediments. USGS field and laboratory measurements of toxic mine waste and organic effluent samples suggest that anthropogenic wastes typically contain finely-divided metal and metal-sulfide particles. The
anoxic environment provided by anthropogenic wastes promotes the growth of anaerobic bacteria, creating a self-reducing environment. We suggest that the finely-divided metal and metal-sulfide particles are the products of bacterial reduction and precipitation. The fine-grained metallic precipitates are ideal targets for a surface-effect electrochemical detection methodology called Induced Polarization (IP). A USGS-patented (1998/2001) marine IP streamer technology has recently been commercialized
and used to map “black smoker” sulfide deposits and their disseminated halos in the Bismarck Sea (2005), and titanium-sand deposits offshore of South Africa (2007). The marine induced polarization system can do this mapping in three dimensions, more rapidly (it is towed at 3 knots) , and with far
higher resolution that land-based measurements or vibracoring. Laboratory-scale studies at the USGS suggest that anthropogenic wastes may display a specific multi-frequency IP spectral signature that may be applicable to waste-deposit mapping.

Lunar & Planetary Science Conference, 2024

Scientific American, Nov 1998

Journal of Geophysical Research, 2004

Journal of Environmental & Engineering Geophysics, Vol. 7, No. 4, p. 143-150., 2002

ArXiv, 2023

INDUCED POLARIZATION AND MAGNETIC RESPONSE OF TITANIUM-BEARING PLACER DEPOSITS IN THE SOUTHEASTERN UNITED STATES, 1985

US Geological Survey Open File Report 85-756, 1985

US Patent and Trademark Office, Jun 11, 2013

"A seawater capacitance detection method for rapidly mapping and characterizing hydrocarbon plume... more "A seawater capacitance detection method for rapidly mapping and characterizing hydrocarbon plumes in seawater, the method comprising:
towing a streamer array having three or more vertically stacked streamer cables at three or more depths, respectively, through a seawater column containing a hydrocarbon plume;
energizing two or more transmitter electrodes on each streamer cable with an electrical current signal, the transmitter electrodes injecting electrical current into the seawater column;
episodically turning off transmission of the electrical current signal;
arranging a plurality of receiver electrodes on each streamer cable into one or more receiver sets, each receiver set sampling a volume of seawater surrounding it and detecting any returned secondary signals produced by a capacitive effect resulting from injecting the electrical current into the seawater column and turning off the transmission of the electrical current signal, and each receiver set successively sampling a larger volume of water as the receiver sets are positioned further away from the transmitter electrodes;
processing the returned secondary signals, for each adjacent pair of receiver sets, by subtracting the smallest volume of seawater from the next smallest volume of seawater to yield a capacitance value of a donut-shaped sampling volume of seawater outside the smallest volume, the receiver sets positioned further away from the transmitter electrodes providing increasingly larger donut-shaped sampling volumes of sampling data of the capacitance of the seawater column through which the streamer cables are towed;
processing and geometrically correcting the capacitance values of the donut-shaped sampling volumes of seawater to yield a frequency-varying final seawater capacitance value for the volume of seawater sampled by each receiver set;
and mapping and characterizing the hydrocarbon plume using the final seawater capacitance values of the receiver sets."

Sea Technology Feature Article, Sep 2012

Offshore Technology Conference, Stavanger, Norway, Proceedings, p. 37-41, 2001

A towed-streamer technology has been developed for mapping placer heavy minerals and dispersed hy... more A towed-streamer technology has been developed for mapping placer heavy minerals and dispersed hydrocarbon plumes in the open ocean. The approach uses induced polarization (IP), an electrical measurement that encompasses several different surface-reactive capacitive and electrochemical phenomena, and thus is ideally suited for mapping dispersed or disseminated targets. The application is operated at sea by towing active electrical geophysical streamers behind a ship; a wide area can be covered in three dimensions by folding tow-paths over each other in lawn-mower fashion. This technology has already been proven in laboratory and ocean settings to detect IP-reactive titanium- and rare-earth (REE) minerals such as ilmenite and monazite. By extension, minerals that weather and accumulate/concentrate by a similar mechanism, including gold, platinum, and diamonds, may be rapidly detected and mapped indirectly- even when dispersed and covered with thick, inert sediment. IP is also highly reactive to metal structures such as pipelines and cables. Currently, the only means for mapping an oil-spill plume is to park a large ship in the ocean and drop a sampling string over the side, requiring hours of time per sampling point. The samples must then be chemically analyzed, adding additional time and expense. We believe that an extension of the marine IP technology could also apply to rapidly mapping both seafloor- blanket and disseminated hydrocarbon plumes in the open ocean, as hydrocarbon droplets in conductive seawater are topologically equivalent to a metal-plates-and-dielectric capacitor. Because the effective capacitance would be frequency-dependent on droplet size, the approach we advocate holds the potential to not only map, but also to characterize the evolution and degradation of such a plume over time. In areas where offshore oil field development has been practiced for extended periods, making IP measurements from a towed streamer may be useful for locating buried - nd exposed pipelines, as well as pipeline leaks. We believe this technique will be a more cost-effective method than drop-sampling to map and monitor hydrocarbon plumes in open ocean settings. A marine induced polarization system was used successfully to map a 15 km × 45 km swath of the ocean floor off eastern South Africa with 3-meter sampling along 200-meter-separated profiles. The survey detected titanium-bearing sands up to 15 meters below the seafloor. From preliminary laboratory work it is apparent that we can extend this technology to monitor significant environmental problems including anthropogenic and industrial waste washed into sensitive estuaries and sounds during storm-water runoff episodes, and also to map and characterize dispersed oil plumes in the seawater column in three dimensions, as well as movement and dispersal of both over time.

Airborne geophysical studies on the American side of the San Pedro Valley of Arizona and Mexico h... more Airborne geophysical studies on the American side of the San Pedro Valley of Arizona and Mexico have allowed us to map depth to crystalline basement in this area where groundwater is critically important (Alley and, whose head lies in northern Mexico, hosts a major US-Mexico migratory bird fly-way. A desire to preserve the surface water in the San Pedro River led to the creation of the San Pedro National Riparian Conservation Area in 1988. To preserve the surface water, one must know something about the aquifer underlying it. On the American side of the basin, time-domain airborne geophysical methods were used to map the relatively conductive groundwater typical of an arid region to depths of 150-400 meters in the absence of human cultural interference. In order to better understand the hydrology of the basin as a whole, geophysical surveying has been extended southward into the Sonoran San Pedro Valley of northern Mexico. An airborne magnetic survey in northern Mexico has been processed to depth-to-magnetic-source, and concatenated to a magnetic data set from southern Arizona to show depth to basement for the San Pedro Valley drainage. We then conducted a scalar Audio-MagneTotelluric (AMT) survey over four different lines in the Sonoran San Pedro basin, and processed these data using a smooth-model inversion to conductivity-vs-depth profiles. As we view the conductivity inversion results, we are in fact visualizing the highly conductive water typical of an arid climate-in effect, we broadly image the saturated sediments. We then used an analytic signal depth-to-source algorithm on magnetic data along the same profiles to constrain the AMT inversion. The result is a unique set of geophysical profiles that clearly show basement structure beneath the Sonoran San Pedro basin to depths of up to 800 meters. These constrained profiles help resolve basement controls on groundwater flow in northern Mexico leading to the US frontier. It is impossible to understand the groundwater regime except in the context of the volcanic and sedimentary history of the region, and neither the geology nor the geophysics can be carried out independently of the other, but the whole together contribute substantially more than the parts.

The San Pedro River Basin is an ecologically significant region, in part because the river hosts ... more The San Pedro River Basin is an ecologically significant region, in part because the river hosts a major North American migratory bird flyway. The importance of surface flow in this river was acknowledged when Congress created the San Pedro National Riparian Conservation Area in 1988. Concern about regional water resources increased almost immediately with calls for the elimination of nearby Fort Huachuca Army base. The Upper San Pedro aquifer of southeastern Arizona is bracketed by crystalline and sedimentary rocks of the Huachuca Mountains on the west and the volcanic and sedimentary rocks of the Mule Mountains and Tombstone Hills on the east (Figure 1). Recharge of the Upper San Pedro Valley aquifer between them is believed to come primarily from the Huachuca Mountains-in fact, most of the aquifer lies to the west of the river on the Fort Huachuca side. Fort Huachuca and the adjacent city of Sierra Vista lie between the Huachuca Mountains and the river, and have been tapping this aquifer for over a century. The historical flow in the river has apparently been affected by water withdrawal by large copper mines in neighboring Mexico beginning in the late 1940s (Brown et al., 1966), but to what extent is unknown. Estimates of groundwater withdrawal versus recharge on the American side of the border, despite conservation efforts by the U. S. Army and local jurisdictions, still suggest a deficit (Pool and Coes, 1999). The groundwater in the area is quite conductive, ranging from 20 to 120 mS/m (Pool and Coes, 1999), making the EM component of the airborne geophysical study a potentially effective means for mapping the groundwater. At issue is how withdrawal by the army base and the nearby cities might affect the integrity of the river; the apparent
iu.s. Geological Survey, 954 National Center, Reston, VA 20192. Email: jwynn@usgs.gov. 2U.S. Geological Survey Southwest Field Office, Tucson, AZ. E-mail: mbultman@usgs.gov. 3Fugro Airborne, 2060 Walkley Road, Ottawa, Ontario, Canada, KlG 3P5. E-mail: jlemieux@fugroairborne.com.
recharge deficit has given rise to claims that they jointly threaten the integrity of the Riparian Conservation Area. For these reasons, the U. S. Army funded two airborne geophysical surveys over the Upper San Pedro Valley (Figure 1). Both surveys were conducted under contract by FugroGeoterrex using their proprietary GeoTEM® system: timedomain airborne electromagnetic (AEM) and magnetic surveys were acquired simultaneously. The 1997 survey covered the center of the area of interest, and the 1999 survey extended this coverage north, east, and west to an aggregate of about 1000 km2 of coverage. The resulting data have provided valuable information on the aquifer, as well as the complex basement structure underlying the modem San Pedro Valley and the Tombstone volcanic complex, both of which may, in part, constrain the surface water flow in the river.

Prince William Forest Park is situated at the northeastern end of the Virginia Gold-Pyrite belt n... more Prince William Forest Park is situated at the northeastern end of the Virginia Gold-Pyrite belt northwest of the town of Dumfries, VA. The U. S. Marine Corps Reservation at Quantico borders the park on the west and south, and occupies part of the same watershed. Two abandoned mines are found within the park: the Cabin Branch pyrite mine, a historic source of acid mine drainage, and the Greenwood gold mine, a source of mercury contamination. Both are within the watershed of Quantico Creek (Fig.1). The Cabin Branch mine (also known as the Dumfries mine) lies about 2.4 km northwest of the town of Dumfries. It exploited a 300 meter-long, lens-shaped body of massive sulfide ore hosted by metamorphosed volcanic rocks; during its history over 200,000 tons of ore were extracted and processed locally. The site became part of the National Capitol Region of the National Park Service in 1940 and is currently managed by the National Park Service. In 1995 the National Park Service, in cooperation with the Virginia Department of Mines, Minerals, and Energy reclaimed the Cabin Branch site.

An airborne electromagnetic survey was conducted over 1,000 square kilometers of southern Arizona... more An airborne electromagnetic survey was conducted over 1,000 square kilometers of southern Arizona to map the groundwater beneath the San Pedro Basin. This basin hosts the headwaters of the San Pedro River, part of one of the San Pedro Riparian Conservation Area, and a critical element of one of four major North American migratory bird flyways. The survey revealed complex three-dimensional structures in water-hosting sediments and regional faults.

Evaluation of potential high-level nuclear waste repository sites is an area where geophysical ca... more 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.

US Geological Survey Professional Paper 1674, 2006

ABSTRACT This report summarizes the results of two airborne geophysical surveys conducted in the... more ABSTRACT
This report summarizes the results of two airborne geophysical surveys conducted in the upper San Pedro Valley of southeastern Arizona in 1997 and 1999. The combined surveys cover about 1,000 square kilometers and extend from the Huachuca Mountains on the west to the Mule Mountains and Tombstone Hills on the east and from north of the Babocomari River to near the Mexican border on the south. The surveys included the acquisition of high-resolution magnetic data, which were used to map depth to the crystalline basement rocks underlying the sediments filling the basin. The magnetic inversion results show a complex basement morphology, with sediment thickness in the center of the valley ranging from ~237 meters beneath the city of Sierra Vista to ~1,500 meters beneath Huachuca City and the Palominas area near the Mexican border. The surveys also included acquisition of 60-channel time-domain electromagnetic (EM) data. Extensive quality analyses of these data, including inversion to conductivity vs. depth (conductivity-depth-transform or CDT) profiles and comparisons with electrical well logs, show that the electrical conductor mapped represents the subsurface water-bearing sediments throughout most of the basin.

In a few places (notably the mouth of Huachuca Canyon), the reported water table lies above where the electrical conductor places it. These exceptions appear to be due to a combination of outdated water-table information, significant horizontal displacement between the wells and the CDT profiles, and a subtle calibration issue with the CDT algorithm apparent only in areas of highly resistive (very dry) overburden. These occasional disparities appear in less than 5 percent of the surveyed area. Observations show, however, that wells drilled in the thick unsaturated zone along the Huachuca Mountain front eventually intersect water, at which point the water rapidly rises high into the unsaturated zone within the wellbore. This rising of water in a wellbore implies some sort of confinement below the thick unsaturated zone, a confinement that is not identified in the available literature. Occasional disparities notwithstanding, maps of the electrical conductor derived from the airborne EM system provide a synoptic view of the presence of water underlying the upper San Pedro Valley, including its three-dimensional distribution. The EM data even show faults previously only inferred from geologic mapping.

The magnetic and electromagnetic data together appear to show the thickness of the sediments, the water in the saturated sediments down to a maximum of about 400 meters depth, and even places where the main ground-water body is not in direct contact with the San Pedro River. However, the geophysical data cannot reveal anything directly about hydraulic conductivity or ground-water flow. Estimating these characteristics requires new hydraulic modeling based in part on this report.

One concern to reviewers of this report is the effect that clays may have on the electrical conductor mapped with the airborne geophysical system. Although the water in the basin is unusually conductive, averaging 338 microsiemens per centimeter, reasoning cited below suggests that the contribution of clays to the overall conductivity would be relatively small. Basic principles of sedimentary geology suggest that silts and clays should dominate the center of the basin, while sands and gravels would tend to dominate the margins. Although clay content may increase the amplitude of the observed electrical conductors somewhat, it will not affect the depths to the conductor derived from depth inversions. Further, fine-grained sediments generally have higher porosity and tend to lie toward a basin center, a fact in general agreement with the observed geophysical data."

Geophysics-The Leading Edge, 2002

US Geological Survey Professional Paper 1674, 2006

The Venezuelan Guayana Shield comprises the Precambrian terrane of the southern and eastern half ... more The Venezuelan Guayana Shield comprises the Precambrian
terrane of the southern and eastern half of Venezuela
and encompasses more than 415,000 km2. This report
describes the geology and geophysics of the Venezuelan
Guayana Shield and presents a mineral resource assessment
of the area. It includes a geographic map, geologic and
tectonic map, simple Bouguer gravity anomaly map, sidelooking
airborne radar image, two mineral occurrences
maps, and two permissive domain maps. The report is a
product of a cooperative project on the Venezuelan Guayana
Shield between the U.S. Geological Survey and the
Corporacio'n Venezolana de Guayana, Te'cnica Minera,
C.A., that was begun in 1987 and concluded in 1991.

Nook Books, 2011

A summary of the geology of Venezuela, and how it underlies modern political development includin... more A summary of the geology of Venezuela, and how it underlies modern political development including the rise of Hugo Chavez. The southern half of Venezuela is jungle-covered, with almost no road access for an area the size of Texas - but it is enormously endowed with mineral wealth including gold, iron, bauxite, and rare earth elements.

US Geological Survey Bulletin 1960, 1991

ABSTRACT Early Proterozoic rocks typical of greenstone-granite terranes underlie eastern Venez... more ABSTRACT
Early Proterozoic rocks typical of greenstone-granite terranes underlie eastern Venezuela. The greenstone-belt rocks in the NB-20-4 quadrangle (1 o by 11/2°) consist of submarine sequences with mafic-ultramafic intrusions, mafic to felsic
volcanic, volcaniclastic, and turbiditic rocks, and chemical and detrital sedimentary rocks. Granitic rocks and granitic gneiss of the Supamo Complex intrude the greenstone belts. In the greenstone-belt rocks, the metamorphic grade ranges from
subgreenschist facies in the interior of belts to amphibolite facies at contacts with intrusions. Diabase dikes and a ringlike complex of diabase or gabbro, such as the Laguna dike and Nuria complex, respectively, are younger than the greenstone-granite rocks. Positive aeromagnetic anomalies throughout the quadrangle coincide closely with mapped greenstone-belt rocks and show a larger proportion of greenstone-belt rocks than is shown on the geologic map, especially on the western
margins of the greenstone belts. In one example, magnetic data demonstrate that the greenstone belt extends as much as 15 km (kilometers) farther west-southwest of the westernmost geologically mapped outcrop; the surficial area covered by greenstone-belt rocks may actually be more than 30 percent higher than what is shown on the geologic map. Structural data collected from the field and interpretation of side-looking airborne radar and aeromagnetic data have identified several major fault or shear zones in the quadrangle.
Several mineral-deposit models are possible in quadrangle NB-20-4, based on the geologic, geophysical, and structural characteristics of the rocks and on known mineral occurrences. These mineral-deposit models include: (1) low-sulfide
gold-quartz veins; (2) placer gold with platinum-group elements (PGE); (3) dunitic nickel-copper; (4) kuroko-type massive sulfide; (5) laterite-type bauxite; (6) secondarily enriched volcanogenic manganese; and possibly (7) Homestake-
type gold deposits. Between 16 and 27 low-sulfide gold-quartz vein-type deposits may be present within the quadrangle based on a model of mineral-deposit density
within a given area of greenstone-belt rocks in similar geologic environments around the world. At present, two gold vein deposits are being exploited within the quadrangle, and one other lode deposit at the Vuelvan Caras-Purgatorio gold
district, which may be more representative of a gold-rich porphyry copper deposit, is also being worked. Placer-gold deposits are also being mined within the quadrangle, as evidenced by small-scale mining activity."
Manuscript approved for publication September 27, 1990.

US Geological Survey Bulletin 2062, 1992

ABSTRACT The Venezuelan Guayana Shield comprises the Pre-cambrian terrane of the southern and ea... more ABSTRACT
The Venezuelan Guayana Shield comprises the Pre-cambrian terrane of the southern and eastern half of Venezuela and encompasses more than 415,000 km2. This report describes the geology and geophysics of the Venezuelan Guayana Shield and presents a mineral resource assessment of the area. It includes a geographic map, geologic and tectonic map, simple Bouguer gravity anomaly map, side-looking airborne radar image, two mineral occurrencesmaps, and two permissive domain maps. The report is a product of a cooperative project on the Venezuelan Guayana Shield between the U.S. Geological Survey and the Corporaci6n Venezolana de Guayana, Tecnica Minera, C.A., that was begun in 1987 and concluded in 1991.

Global Tectonics and Metallogeny, Vol 7, No 2, P. 95-102., 1999

Geoarchaeology, 2007

Geophysical methods have been used with increasing frequency in archaeology since 1946; aerial ph... more Geophysical methods have been used with increasing frequency in archaeology since 1946; aerial photography has been used since 1919. The geophysical methods that are most commonly used at present are electrical resistivity, magnetics, and ground-probing radar. Magnetic detectors, particularly when used in
a gradient mode or with a continuously recording base station, are used at almost all sites where any geophysical methods are used. Portable, noncontacting electromagnetic soil-conductivity systems are also being increasingly used because of their very high rate of data acquisition. Less commonly used methods
include self-potential (sometimes called spontaneous potential), microgravity, radiometric, thermal infrared imagery, and sonic or seismic techniques. Recent developments in image processing and graphic representation have contributed substantially to the archaeologist’s ability to do “rescue archaeology,” that is, to carry out high-speed, nondestructive reconnaissance surveys for ancient human cultural evidence in advance of modern industrial development.

Journal of Field Archaeology, 11, No. 2, p. 195-204., 1984

Geological Society of America Special Volume on Geoarchaeology, 1990

US Geological Survey Data Series 901, 2015

We have observed several new features in recent controlled-source audio-frequency magnetotelluric... more We have observed several new features in recent controlled-source audio-frequency magnetotelluric (CSAMT) soundings on and around Mount St. Helens, Washington State, USA. We have identified the approximate location of a strong electrical conductor at the edges of and beneath the 2004–08 dome. We interpret this conductor to be hot brine at the hot-intrusive-cold-rock interface. This contact can be found within 50 meters of the receiver station on Spine 5, which extruded between April and July of 2005. We have also mapped separate regional and glacier-dome aquifers, which lie one atop the other, out to considerable distances from the volcano.

The array of geophysical technologies used in volcano hazards studies-some developed originally o... more The array of geophysical technologies used in volcano hazards studies-some developed originally only for volcano monitoring-ranges from satellite remote sensing including InSAR to leveling and EDM surveys, campaign and telemetered GPS networks, electronic tiltmeters and strainmeters, airborne magnetic and electromagnetic surveys, short-period and broadband seismic monitoring, even microphones tuned for infrasound. They include virtually every method used in resource exploration except large-scale seismic reflection. By " geophysical " we include both active and passive methods as well as geodetic technologies. Volcano monitoring incorporates telemetry to handle high-bandwith cameras and broadband seismometers. Critical geophysical targets include the flux of magma in shallow reservoir and lava-tube systems, changes in active hydrothermal systems, volcanic edifice stability, and lahars. Since the eruption of Mount St. Helens in Washington State in 1980, and the eruption at Pu'u O'o in Hawai'i beginning in 1983 and still continuing, dramatic advances have occurred in monitoring technology such as " crisis GIS " and lahar modeling, InSAR interferograms, as well as gas emission geochemistry sampling, and hazards mapping and eruption predictions. The ongoing eruption of Mount St. Helens has led to new monitoring technologies, including advances in broadband Wi-Fi and satellite telemetry as well as new instrumentation. Assessment of the gap between adequate monitoring and threat at the 169 potentially dangerous Holocene volcanoes shows where populations are dangerously xposed to volcanic catastrophes in the United States and its territories. This paper focuses primarily on Hawai'ian volcanoes and the northern Pacific and Cascades volcanoes. The US Geological Survey, the US National Park System, and the University of Utah cooperate in a program to monitor the huge Yellowstone volcanic system, and a separate observatory monitors the restive Long Valley caldera in collaboration with the US Forest Service.

This report describes a series of geoelectrical soundings carried out on and near Mount St. Helen... more This report describes a series of geoelectrical soundings carried out on and near Mount St. Helens volcano,
Washington, in 2010–2011. These soundings used a controlled-source audio-frequency magnetotelluric (CSAMT) approach (Zonge and Hughes, 1991; Simpson and Bahr, 2005). We
chose CSAMT for logistical reasons: It can be deployed by helicopter, has an effective depth of penetration of as much as 1 kilometer, and requires less wire than a Schlumberger sounding.
This Data Series provides the edited data for these CSAMT soundings as well as several different types of 1-D inversions (where the signal data are converted to conductivity-versus-depth models). In addition, we include a map showing station locations on and around the volcano and the Pumice Plain to the north. The apparent conductivity (or its inverse, apparent resistivity) measured by a geoelectrical system is caused by several factors. The most important of these are water-filled rock porosity and the presence of water-filled fractures;
however, rock type and minerals (for instance, sulfides and clay content) also contribute to apparent conductivity. In situations with little recharge (for instance, in arid regions), variations in ionic content of water occupying pore space and fractures sampled by the measurement system must also be factored
in (Wynn, 2006). Variations in ionic content may also be present in hydrothermal fluids surrounding volcanoes in wet regions. In unusual cases, temperature may also affect apparent conductivity (Keller, 1989; Palacky, 1989). There is relatively little hydrothermal alteration (and thus fewer clay minerals that might add to the apparent conductivity) in the eruptive products of Mount St. Helens (Reid and others, 2010), so conductors observed in the Fischer, Occam, and Marquardt inversion results later in this report are thus believed to map zones with significant water content. Geoelectrical surveys thus
have the potential to reveal subsurface regions with significant groundwater content, including perched and regional aquifers. Reid and others (2001) and Reid (2004) have suggested that groundwater involvement may figure in both the scale and the character of some if not all volcanic edifice collapse events.

Abstract This report describes a series of geoelectrical soundings carried out on and near Mount ... more Abstract
This report describes a series of geoelectrical soundings carried out on and near Mount St. Helens volcano, Washington, in 2010–2011. These soundings used a controlled-source audio-frequency magnetotelluric (CSAMT) approach (Zonge and Hughes, 1991; Simpson and Bahr, 2005). We chose CSAMT for logistical reasons: It can be deployed by helicopter, has an effective depth of penetration of as much as 1 kilometer, and requires less wire than a Schlumberger sounding.

This Data Series provides the edited data for these CSAMT soundings as well as several different types of 1-D inversions (where the signal data are converted to conductivity-versus-depth models). In addition, we include a map showing station locations on and around the volcano and the Pumice Plain to the north.

The apparent conductivity (or its inverse, apparent resistivity) measured by a geoelectrical system is caused by several factors. The most important of these are water-filled rock porosity and the presence of water-filled fractures; however, rock type and minerals (for instance, sulfides and clay content) also contribute to apparent conductivity. In situations with little recharge (for instance, in arid regions), variations in ionic content of water occupying pore space and fractures sampled by the measurement system must also be factored in (Wynn, 2006). Variations in ionic content may also be present in hydrothermal fluids surrounding volcanoes in wet regions. In unusual cases, temperature may also affect apparent conductivity (Keller, 1989; Palacky, 1989). There is relatively little hydrothermal alteration (and thus fewer clay minerals that might add to the apparent conductivity) in the eruptive products of Mount St. Helens (Reid and others, 2010), so conductors observed in the Fischer, Occam, and Marquardt inversion results later in this report are thus believed to map zones with significant water content. Geoelectrical surveys thus have the potential to reveal subsurface regions with significant groundwater content, including perched and regional aquifers. Reid and others (2001) and Reid (2004) have suggested that groundwater involvement may figure in both the scale and the character of some if not all volcanic edifice collapse events. Ongoing research by the U.S. Geological Survey (USGS) and others aims to better understand the contribution of groundwater to both edifice pore pressure and rock alteration as well as its direct influence on eruption processes by violent interaction with magma (Schmincke, 1998).

US Geological Survey Data Series 830, 2014

"ABSTRACT Newberry Volcano in central Oregon is a 3,100-square-kilometer (1,200-square-mile) shi... more "ABSTRACT
Newberry Volcano in central Oregon is a 3,100-square-kilometer (1,200-square-mile) shield-shaped composite volcano, occupying a location east of the main north-south trend of the High Cascades volcanoes and forming a transition between the High Lava Plains subprovince of the Basin and Range Province to the east and the Cascade Range to the west. Magnetic, gravity, and radiometric data have been gathered and assessed for the region around the volcano. These data have widely varying quality and resolution, even within a given dataset, and these limitations are evaluated and described in this release.

Publicly available gravity data in general are too sparse to permit detailed modeling except along a few roads with high-density coverage. Likewise, magnetic data are also unsuitable for all but very local modeling, primarily because available data consist of a patchwork of datasets with widely varying line-spacing. Gravity data show only the broadest correlation with mapped geology, whereas magnetic data show moderate correlation with features only in the vicinity of Newberry Caldera. At large scales, magnetic data correlate poorly with both geologic mapping and gravity data. These poor correlations are largely due to the different sensing depths of the two potential fields methods, which respond to physical properties deeper than the surficial geology. Magnetic data derive from rocks no deeper than the Curie-point isotherm depth (10 to 15 kilometers, km, maximum), whereas gravity data reflect density-contrasts to 100 to 150 km depths. Radiometric data from the National Uranium Resource Evaluation (NURE) surveys of the 1980s have perhaps the coarsest line-spacing of all (as much as 10 km between lines) and are extremely “noisy” for several reasons inherent to this kind of data. Despite its shallow-sensing character, only a few larger anomalies in the NURE data correlate well with geologic mapping."""

Proceedings, Japan-Kamchatka-Alaska Scientific Project, 2006

ABSTRACT "Geophysical and other technologies used to monitor volcanoes in the Cascades Volcanoes... more ABSTRACT
"Geophysical and other technologies used to monitor volcanoes in the Cascades Volcanoes of North America can be partitioned into a commonly used category, and a less-routinely-used or still largely experimental category. A few potentially useful technologies routinely used in mineral resource exploration are yet to be tested. This presentation will focus primarily on geophysical instrumentation, including telemetered cameras and thermal imagery, and will also briefly outline our use of airborne gas-sampling, Digital Elevation Models (DEMs), and InSAR.

The more common technical means for monitoring Pacific Cascades volcanoes include passive seismic (short-period and broadband, each with their respective advantages and limitations), deformation (campaign-style and continuous GPS, tilt meters, and periodic ground- truthing leveling surveys), airborne and fumerole gas-sampling, telemetered cameras and helicopter-mounted thermal (FLIR) imaging systems, satellite thermal and ash monitoring, DEMs, and InSAR interferometry. Less-common means include unmanned autonomous vehicles (UAVs), airborne magnetic and electromagnetic surveys, acoustic flow monitors (AFMs), and infra-sound.

Seismic methods are the historical workhorse of volcano monitoring. The more recent but relatively power-hungry broadband devices allow us to identify low-frequency (1-2 Hz, long-period or LP) volcanic tremor generally considered evidence of fluid movement at depth. Older short-period seismic systems allow us to identify brittle-rock failure that usually is the
immediate precursor for an eruption; these are less expensive and draw less power, so are more easily deployed. Recent developments in continuous GPS (CGPS) technology in principle allow us to detect inflation of a volcanic edifice long before any seismicity is apparent. In fact, deformation was first observed at theThree Sisters volcanic center in Oregon several years before
the first cluster of VT earthquakes; deformation was observed at Augustine volcano about four months before the first precursory seismic events, which themselves appeared only a few weeks
before the first eruption. Inflation inferred from CGPS units was approximately coeval with the onset of deep LP earthquakes beneath Mauna Loa volcano in Hawaii in 2004.

Airborne COSPEC and ground-based Fourier Transform Infra-Red (FTIR) gas measurements are useful for identifying uniquely magmatic gas species such as SO2 and HF. Sudden changes in the volume being produced can potentially warn of an impending explosion. However, unusually low levels of CO2 and SO2 at Mount St. Helens beg the question of what is driving the current eruption (dacite extruding at about ~1 cubic meter/day)? If not exolving gas pressurization, then isostatic loads or recharge at depth?

Ultimately volcanologists want to see what is going on, and there is a large array of technologies now available for this purpose. These include helicopter-mounted thermal imaging (FLIR) systems, telemetered cameras, InSAR, and DEMs to quantify dome growth; and satellite imagery to identify ash plumes (split-window IR) and thermal hot spots on remote volcanoes.
Most of these require relatively cloud-free skies, something notably missing for at least half of any given year in the Cascades Range. While InSAR allows us to gather a synoptic view of an
inflating or deflating volcanic system even through clouds, this approach depends on the infrequent availability of satellite radar images that can be differenced against each other, and must be
considered a long-term monitoring methodology. We are now in the final stages of purchasing a powerful portable Doppler radar system, which should at last give us real-time imagery of any
developing ash plume - even through clouds.

Less commonly used technology includes automated Acoustic Flow Monitors (currently established around Mount Rainier), airborne time-domain electromagnetic and magnetic surveys (used to map hydrothermally altered rock and thus edifice stability at Mount Rainier), unmanned autonomous aircraft (tried at Mount St. Helens during the Fall and Winter of 2004-2005), gravimetry (tested at Medicine Lake Volcano in 2004), and infrasound. Additional methods used in resource exploration, such as borehole geophysics and tomography, large-loop time- domain
EM soundings, telluric-current profiles, etc., have not yet been attempted at Cascades Range volcanoes.

Safety considerations for scientists working on and near active volcanoes have come to the forefront of our thinking in recent years. It is transparently unwise to install new labor-
intensive instrumentation on a volcano that has reawakened and is already restive. Nence, we have developed self-contained (power, instrumentationn, telemetry - so-called “Spider”) instrumentation packages that can be deployed using a helicopter at minimal risk to scientists, technicians, and pilots. Taking a longer view, however, the USGS has proposed a National Volcano Early Warning System (“NVEWS”) to instrument the most dangerous volcanoes before they awaken. Great care and thought have gone into a prioritizing methodology for ranking the169 Holocene volcanoes in the US and its territories.
"

Environmental & Engineering Geophysical Society, Seattle, WA, April 2-6, 2006, p. 174-183, 2006

Greens Creek, one of the largest producing volcanogenic massive sulfide (VMS) deposits in southea... more Greens Creek, one of the largest producing volcanogenic massive sulfide (VMS) deposits in southeast Alaska, is found on north-central Admiralty Island. It and other known VMS prospects in the region are found only in Triassic-age Hyd Group volcanic rocks. Because most of the region is covered by dense vegetation, water, and tidal mud-flats, we have used ground and airborne geophysical information to develop geophysical signatures for Hyd and other accreted Alexander Terrane rocks in the region. This has dramatically improved our geologic mapping efforts, therefore allowing more efficient exploration for other Greens Creek type VMS deposits.

Triassic Hyd Group rocks in southeastern Alaska are the most likely target for a volcanogenic mas... more Triassic Hyd Group rocks in southeastern Alaska are the most likely target for a volcanogenic massive sulfide (VMS) deposit according to available information. However, because of difficult access and extensive cover, the geology in this region is not well known in detail, and available maps have necessarily been of a reconnaissance nature. Ground and airborne geophysical methods offer perhaps the most cost-effective means for improving the geological mapping, as long as the key geologic units (including the Hyd Group) can be differentiated. This appears to be possible, despite the complication of regional metamorphism which can change both magnetite content as well as resistivity of the key units. Careful selection of ground profiles in areas where the geology is well known has allowed us to develop a geophysical signatures matrix for a large section of southeastern Alaska from Admiralty Island in the north to Prince of Wales Island in the south. We used the ground geophyical signatures with the airborne geophysical data to develop a predlctlve geophysical model for the key geologic units, and these in turn have been used to substantially modify the earlier geologic maps. This has resulted in an increase of more than 30% in ground now known to be underlain by Triassic Hyd Group rocks, with a concomitant increase in prospective land.

Global Tectonics & Metallogeny, Vol. 8, No. 1, p. 1-4, 2003

Alaska Miners Association Powerpoint Presentation, 2000, 2000

ABSTRACT Work began in 1995 on Admiralty Island, then progressed south with an airborne magnetic... more ABSTRACT
Work began in 1995 on Admiralty Island, then progressed south with an airborne magnetic and ElectroMagnetic (EM) survey (flown in 1996) to the Duncan-Zarembo area, and is now focused on following up a 1999 airborne mag/EM survey on Prince of Wales Island.
The driving forces behind all this work are the forced cutbacks in logging permits, and the search for a new Greens Creek-type deposit as a local economic alternative to logging
Areas with potential for volcanogenic massive sulfide (VMS) deposits are the targets of the airborne geophysics.

Laboratory and field measurements were made in a study of a small number of chromite deposits in ... more Laboratory and field measurements were made in a study of a small number of chromite deposits in the Josephine ultramafic complex of northwest California, to examine their physical properties and to search for possible diagnostic geophysical signatures. Though the sample was small, the results show that no single geophysical method gives unequivocal identification of buried massive pods of chromite, but that a combination of gravity, magnetics, and seismics, and complex resistivity might be used to explore successfully if used in a systematic fashion. Some of the geophysical signatures appear to be secondary or associative in nature, raising the possibility that a specific method or combination of methods might have to be modified for application in
an area other than where they were developed.

Abstract Undiscovered potash resources in the Central Asia Salt Basin (CASB) of Turkmenistan, Uzb... more Abstract
Undiscovered potash resources in the Central Asia Salt Basin (CASB) of Turkmenistan, Uzbekistan, Tajikistan, and Afghanistan were assessed as part of a global mineral resource assessment led by the U.S. Geological Survey (USGS). The term “potash” refers to potassium-bearing, water-soluble salts derived from evaporite basins, where seawater dried up and precipitated various salt compounds; the word for the element “potassium” is derived from potash. Potash is produced worldwide at amounts exceeding 30 million metric tons per year, mostly for use in fertilizers. The term “potash” is used by industry to refer to potassium chloride, as well as potassium in sulfate, nitrate, and oxide forms (Neuendorf and others, 2005). For the purposes of this assessment, the term “potash” refers to potassium ores and minerals and potash ore grades. Resource and production values are usually expressed by industry in terms of K2O (potassium oxide) or muriate of potash (KCl, potassium chloride).
The CASB hosts significant discovered potash resources and originated in an inland sea during Late Jurassic time. Seawater flowed into the CASB, mostly from its extreme northwestern margin near the modern Caspian Sea, during several evaporation episodes that deposited at least five different packages of evaporites, with virtually all potash in the second and fourth packages. In this study, the CASB was subdivided into three tracts (permissive areas) for evaluation: the Amu Darya tract in the west, the Gissar tract in the center, and the Afghan-Tajik tract in the east. The Gissar and Amu Darya tracts were quantitatively assessed, whereas the Afghan‑Tajik tract was only qualitatively assessed because of the commonly extreme depth (as deep as 7 km) of the Jurassic salt, extensive deformation, and a lack of known potash deposits.
Two approaches were used to estimate amounts of undiscovered potash in the CASB. Stratabound evaporite deposits in the Amu Darya tract were evaluated using an Adaptive Geometric Estimation (AGE) approach, which estimates in-place potash volumes and tonnages. The Gissar tract was evaluated by using the AGE approach for stratabound deposits and the three-part form of assessment of Singer and Menzie (2005) for discrete halokinetic deposits. In the three-part form of assessment, numbers of undiscovered deposits were estimated and combined with grade and tonnage models to probabilistically forecast the amount of undiscovered potash. The Amu Darya tract is estimated to contain 38 billion metric tons (Bt) of undiscovered potash as K2O by using the AGE approach for stratabound deposits. The hybrid stratabound-halokinetic Gissar tract is estimated to contain between 1 and 16 Bt of undiscovered potash as K2O.
Chapter 1 of this report provides an overview of the history of the CASB and summarizes evaporite potash deposition, halokinesis, and dissolution processes that have affected the current distribution of potash-bearing salt in the CASB. Chapter 2 describes the Gissar tract, an uplifted region that contains a mix of stratabound and halokinetic potash deposits and all of the discovered and exploited potash deposits of the CASB. Chapter 3 describes the Amu Darya tract, where evaporite deposits remain flat-lying and undeformed since their original deposition. Chapter 4 describes the highly deformed and compressed Afghan‑Tajik tract and what is known of the deeply-buried Jurassic salt. Chapter 5 describes the spatial databases included with this report, which contain a collection of CASB potash information. Appendixes A and B summarize descriptive models for stratabound and halokinetic potash-bearing salt deposits, respectively. Appendix C summarizes the AGE method used to evaluate the Gissar and Amu Darya tracts. Appendixes D and E contain grade and thickness data for the Gissar and Amu Darya tracts. Appendix F provides the SYSTAT script used to estimate undiscovered K2O in a CASB tract. Appendix G provides a potash glossary, and

Magnetic, satellite (GRACE) gravity, and radiometric data were acquired for western Afghanistan a... more Magnetic, satellite (GRACE) gravity, and radiometric data were acquired for western Afghanistan and compared against each other. The objective was to help isolate phosphate sources in the west Afghanistan region where older Russian radiometric data were available. Because phosphate correlates well with uranium in other parts of the ancient Tethyan Sea (Wynn, 1993, 1996; see figs. 19 and 20), the emphasis in this report is primarily on uranium.

Porphyry copper deposits result from the complex interactions and feedbacks of many processes. Ow... more Porphyry copper deposits result from the complex interactions and feedbacks of many processes. Owing to the complexity, a succinct definition that includes the essential attributes of this deposit class is elusive. Consequently, this descriptive model uses a working definition of a porphyry copper deposit. A porphyry copper deposit is
1. One wherein copper-bearing sulfides are localized in a network of fracture-controlled stockwork veinlets and as disseminated grains in the adjacent altered rock matrix;
2. Alteration and ore mineralization at 1-4 km depth are genetically related to magma reservoirs emplaced into the shallow crust (6-8+ km), predominantly intermediate to silicic in composition, in magmatic arcs above subduction zones;
3. Intrusive rock complexes that are emplaced immediately before porphyry deposit formation and that host the deposits are predominantly in the form of upright vertical cylindrical stocks and/or complexes of dikes;
4. Zones of phyllic-argillic and marginal propylitic alteration overlapping and surrounding a potassic alteration assemblage; and,
5. Copper may also be introduced during overprinting phyllic-argillic alteration events.

Very low frequency electromagnetic, magnetic, and induced polarization methods have been used to ... more Very low frequency electromagnetic, magnetic, and induced polarization methods have been used to map gold-bearing metasediments at the Haile gold mine in South Carolina. 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 these metasediments and also fill faults that offset them. The induced polarization method allows us to examine the mineralized metasediments in two
dimensions by giving us 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.

Abstract As part of a larger study, the U.S. Geological Survey undertook a study to identify the ... more Abstract
As part of a larger study, the U.S. Geological Survey undertook a study to identify the
potential for phosphate deposits in Afghanistan. As part of this study, a geographic information
system was constructed containing a database of phosphate occurrences in Afghanistan and adjacent
countries, and a database of potential host lithologies compiled from 1:1,000,000 scale maps. Within
Afghanistan, a handful of known occurrences and reports indicate the presence of phosphate in
Permian, Cretaceous, and Paleogene sediments and in carbonatite. With the exception of the
Khanneshin carbonatite, very little is known about these occurrences. In the countries surrounding
Afghanistan, economic phosphate is known to occur in Cambrian, Devonian, and Paleogene
sediments and in Kiruna-type Fe-apatite deposits. Many of the host units may extend into
Afghanistan or equivalent units may be present. Although the possibility of economic phosphate
deposits exist for Afghanistan, the need for detailed exploration for phosphate, the remoteness of
some locations, and the probability that a deposit would not be exposed at the surface mean that one
or more deposits are not likely to be identified in the near future. Even if a phosphate-bearing deposit
is identified in Afghanistan, it is not clear if the probable size, thickness, and grade ranges would
allow economic development of the hypothesized resource.

US Geological Survey Bulletin 1960, 1991

ABSTRACT Early Proterozoic rocks typical of greenstone-granite terranes underlie eastern Venezu... more ABSTRACT
Early Proterozoic rocks typical of greenstone-granite
terranes underlie eastern Venezuela. The greenstone-belt rocks
in the NB-20-4 quadrangle (1 o by 11/2°) consist of submarine
sequences with mafic-ultramafic intrusions, mafic to felsic
volcanic, volcaniclastic, and turbiditic rocks, and chemical
and detrital sedimentary rocks. Granitic rocks and granitic
gneiss of the Supamo Complex intrude the greenstone belts. In
the greenstone-belt rocks, the metamorphic grade ranges from
subgreenschist facies in the interior of belts to amphibolite
facies at contacts with intrusions. Diabase dikes and a ringlike
complex of diabase or gabbro, such as the Laguna dike and
Nuria complex, respectively, are younger than the greenstonegranite
rocks. Positive aeromagnetic anomalies throughout the
quadrangle coincide closely with mapped greenstone-belt
rocks and show a larger proportion of greenstone-belt rocks
than is shown on the geologic map, especially on the western
margins of the greenstone belts. In one example, magnetic data
demonstrate that the greenstone belt extends as much as 15 km
(kilometers) farther west-southwest of the westernmost
geologically mapped outcrop; the surficial area covered by
greenstone-belt rocks may actually be more than 30 percent
higher than what is shown on the geologic map. Structural data
collected from the field and interpretation of side-looking
airborne radar and aeromagnetic data have identified several
major fault or shear zones in the quadrangle.
Several mineral-deposit models are possible in
quadrangle NB-20-4, based on the geologic, geophysical, and
structural characteristics of the rocks and on known mineral
occurrences. These mineral-deposit models include: (1) lowsulfide
gold-quartz veins; (2) placer gold with platinum-group
elements (PGE); (3) dunitic nickel-copper; (4) kuroko-type
massive sulfide; (5) laterite-type bauxite; (6) secondarily
enriched volcanogenic manganese; and possibly (7) Homestake-
type gold deposits. Between 16 and 27 low-sulfide
gold-quartz vein-type deposits may be present within the
Manuscript approved for publication September 27, 1990.
quadrangle based on a model of mineral-deposit density
within a given area of greenstone-belt rocks in similar geologic
environments around the world. At present, two gold vein
deposits are being exploited within the quadrangle, and one
other lode deposit at the Vuelvan Caras-Purgatorio gold
district, which may be more representative of a gold-rich
porphyry copper deposit, is also being worked. Placer-gold
deposits are also being mined within the quadrangle, as
evidenced by small-scale mining activity.

US Geological Survey Bulletin 2062, 1993

"The Venezuelan Guayana Shield comprises the Pre- cambrian terrane of the southern and eastern ... more "The Venezuelan Guayana Shield comprises the Pre-
cambrian terrane of the southern and eastern half of Vene-
zuela and encompasses more than 415,000 km2. This report
describes the geology and geophysics of the Venezuelan
Guayana Shield and presents a mineral resource assessment
of the area. It includes a geographic map, geologic and
tectonic map, simple Bouguer gravity anomaly map, side-
looking airborne radar image, two mineral occurrences
maps, and two permissive domain maps. The report is a
product of a cooperative project on the Venezuelan Gua-
yana Shield between the U.S. Geological Survey and the
Corporaci6n Venezolana de Guayana, Tecnica Minera,
C.A., that was begun in 1987 and concluded in 1992."

Orris, Greta J., Dunlap, Pamela, Cocker, Mark D., and Wynn, Jeff, 2013, Challenges and approaches to assessing industrial minerals – the USGS global potash assessment databases: Poster 236-15, Geological Society of America 125th Annual Meeting, 27-30 October 2013, Denver, CO.

Geological Society of America 125th Annual Meeting, Oct 28, 2013

"As part of the U.S. Geological Survey’s Global Mineral Resource Assessment Project (GMRAP), an a... more "As part of the U.S. Geological Survey’s Global Mineral Resource Assessment Project (GMRAP), an assessment of potash was undertaken. Two major components of this effort are a comprehensive database of over 950 potash deposits and occurrences and a tract database that identifies 84 areas that have some potential for undiscovered potash resources.
The database of potash deposits and occurrences contains more than 900 site records. This compilation of was a major part of our research effort and is based on collecting and translating well over 2,500 articles, books, and websites. The resulting potash database includes location, age, deposit geology, lithology, mineralogy, geologic setting, size and grade, and references.
Using the potash deposits and occurrences database and other geologic information compiled in the earlier stages of the potash assessment, tracts were delineated for more than 80 areas worldwide where undiscovered potash resources may occur. This study focused primarily on evaporite-hosted potash deposits; specifically stratabound potash-bearing salt and halokinetic potash-bearing salt deposits. Potash resources appear to be widely distributed, although potash does not occur in every salt-bearing basin. Fewer than half of the known salt basins have any reported potash based on this compilation of potash occurrences. Half of the potash-bearing salt basins may have any real potential for production of potash. Within the tracts delineated in this study, 40 may contain a potash deposit of sufficient size and grade to be of possible economic interest.
The databases developed for the GMRAP Potash Assessment have a continuing use beyond the assessment. In addition to demonstrating the widespread nature of potash mineralization, analysis of the compiled data could lead to a better understanding of potash deposits."

Society of Exploration Geophysics Extended Abstracts MN 1.3, p. 600-602, 1996

SUMMARY Geophysical methods have proven useful for mapping the large phosphate deposits in the ... more SUMMARY
Geophysical methods have proven useful for mapping
the large phosphate deposits in the Al-Jalamid region of
northern Saudi Arabia. They were used as an integral
part of the mine feasibility study completed there in 1992.
Friability (which affects economic value) and phosphate
content can be rapidly determined using caliper and
portable gamma-ray logging tools. Once the relationship
between the gamma-ray count rate and phosphate
content are established, integration of gamma-ray activity
over the extent of the drillhole provides a rapid estimate
of the phosphate resource. The limits of the economic
deposit can thus be fairly easily outlined. At the
weathering horizon the ratio between the gamma-ray
activity and phosphate content changes substantially, and
refraction seismics and the caliper log are essential for
knowing where this transition takes place.
The Al-Jalamid area is a featureless, wind-swept, sandcovered
plain. Extensive drilling experience, however,
has shown that this deceptively flat surface masks a karst
terrane, honeycombed with cavities, as circulation is lost
in 25%-30% of drillholes initiated. Microgravity profiles
have proven more useful than refraction seismics for
locating the hidden cavities. Since these cavities are
encountered throughout the Al-Jalamid area, geophysical
methods will be an essential tool in the development of a
mine and its associated mill site.

Symposium on the Application of Geophysics to Engineering and Environmental Problems 2003, 2003

Journal of Environmental and Engineering Geophysics, 2002

The Wabar meteorite impact site in central Saudi Arabia, first visited by Henry St. John (Abdulla... more The Wabar meteorite impact site in central Saudi Arabia, first visited by Henry St. John (Abdullah) Philby in 1932, is unique in several ways. It is one of only 17 impact sites on the Earth where part of the original object is still present. The Wabar impact event also took place entirely in sand, permitting a much clearer and simpler reconstruction of the physical processes of a hypervelocity impact. A careful magnetic survey conducted there adds crucial information to this reconstruction: almost none of the [Formula: see text] of the original iron-nickel object remains in or beneath the known impact craters. The magnetic data were difficult to acquire because of the hostile environment, and the processing was non-trivial for what in effect was a magnetic survey of a ferrous junkyard. The event sequence, which took place in just a few seconds, generated a unique binary set of impactite that includes a black glass (90% local sand and 10% meteorite) and a shock-generated, coarsely la...

Economic Geology, 1984

Very low frequency electromagnetic, magnetic, and induced polarization methods. The very low freq... more 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.--Modified journal abstract.

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1974

US Patent 8,463,568, 2016

A system for mapping and characterizing a hydrocarbon plume in seawater by measuring seawater cap... more A system for mapping and characterizing a hydrocarbon plume in seawater by measuring seawater capacitance. Multiple streamer cables are towed in the sea behind a ship, each at a different depth, simultaneously. Each streamer cable includes transmitters and receivers at the free end thereof. The free ends of the streamer cables pass through the plume and the transmitters transmit an electrical current into the plume.
The receivers detect any secondary signals produced by capacitive effects of the hydrocarbon or hydrocarbon and dispersant surrounded by conductive seawater in response to the inducing electrical current. Pre-amplifiers connected to the receivers and a two-step calibration procedure and various grounding and shielding steps provide noise rejection. An electronics system on board the ship processes the secondary signals to provide immediate development of detailed maps of plume location, and to provide tracking and characterization of how the plume changes shape and character over time.

General Comments The paper is well written and easy to understand. The phenomenon of IP is genera... more General Comments The paper is well written and easy to understand. The phenomenon of IP is generally associated with the phenomenon of electrode polarization in which the mode of conduction must change from ionic to electronic at the boundary between a conductive solution and a metallic conductor. A second mechanism for IP is so-called membrane polarization wherein the ionic mobility of anions and cations in solution can differ markedly in the presence of fixed charge associated with broken bonds in platy silicates cause charge build-up in the presence of an applied electric field. The authors have observed a “complex resistivity” associated with an oil-water

The U.S. Geological Survey (USGS) is required by the Alaska National Interest Lands Conservation ... more The U.S. Geological Survey (USGS) is required by the Alaska National Interest Lands Conservation Act (ANILCA, Public Law 96-487) to survey certain Federal lands to determine their mineral resource potential. As part of continuing studies designed to fulfill this responsibility, geochemical, geological and geophysical surveys of the Craig and Dixon Entrance (CDE) 1x3 quadrangles in southeastern Alaska were undertaken by the USGS during the summers of 1983-85, 1989, and 1991. The geochemical data have been reported by Cathrall and others (1993) and Cathrall (1994). A simplified geologic map has been compiled especially for this report based largely on the work of Eberlein and others (1983) and Gehrels (1991, 1992). Brew (1996) also produced a compilation. This report presents available magnetic and gravity data and an interpretation thereof.

Discussion and Reply Comment on "Benefits of the induced polarization geoelectric method to hydrocarbon exploration" "P. Veeken, P. J. Legeydo, Y. A. Davidenko, E. O. Kudryavceva, S. A. Ivanov, and A. Chuyaev, 2009, Geophysics, 74, no. 2, B47-B59…