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At least 217 records · Page 12Linked to original sources
USGS1987

Petrologic characteristics of the 1982 and pre-1982 eruptive products of El Chichon volcano, Chiapas, Mexico

Studies on a suite of rocks from this volcano indicate that the juvenile materials of the 1982 and pre-1982 eruptions of the volcano have essentially the same mineralogy and chemistry. Data suggest that chemical composition changed little over the 0.3 m.y. sample period. Modally, plagioclase is the dominant phenocryst, followed by amphibole, clinopyroxene and minor phases including anhydrite. Plagioclase phenocrysts show complex zoning: the anorthite-rich zones are probably the result of changing volatile P on the magma and may reflect the changes in the volcano's magma reservoir in response to repetitive, explosive eruptive activity.-R.E.S.

Chiapas↗
USGS2001

Vein deposits hosted by plutonic rocks in the Croesus Stock and Hailey gold belt mineralized areas, Blaine County, Idaho

Mineral deposits in the Croesus and Hailey gold belt mineralized areas in Blaine County, south-central Idaho, are preciousand base-metal quartz veins that are part of a family of vein deposits spatially and temporally associated with the Idaho batholith. Historic production from these veins has been mainly gold and silver. Host rocks are older border phase plutons of the Idaho batholith that are characterized by more potassium and less sodium as compared to rocks from the main body of the batholith to the west. Host structures are reverse faults that have moderate to shallow dips to the northeast and high-angle normal faults that also strike northwest. The veins are characterized by several generations of quartz and generally sparse sulfide minerals; gold is associated with late-stage comb quartz. The precious-metal ore bodies are in a series of shoots, each of which is as much as 8 ft in width, 400 ft in breadth, and 1,000 ft in pitch length.

Bulletin↗
USGS1984

Magmatic inclusions in rhyolites, contaminated basalts, and compositional zonation beneath the Coso volcanic field, California

Basaltic lava flows and high-silica rhyolite domes form the Pleistocene part of the Coso volcanic field in southeastern California. The distribution of vents maps the areal zonation inferred for the upper parts of the Coso magmatic system. Subalkalic basalts (<50% SiO 2 ) were erupted well away from the rhyolite field at any given time. Compositional variation among these basalts can be ascribed to crystal fractionation. Erupted volumes of these basalts decrease with increasing differentiation. Mafic lavas containing up to 58% SiO 2 , erupted adjacent to the rhyolite field, formed by mixing of basaltic and silicic magma. Basaltic magma interacted with crustal rocks to form other SiO 2 -rich mafic lavas erupted near the Sierra Nevada fault zone. Several rhyolite domes in the Coso volcanic field contain sparse andesitic inclusions (55–61% SiO 2 ). Pillow-like forms, intricate commingling and local diffusive mixing of andesite and rhyolite at contacts, concentric vesicle distribution, and crystal morphologies indicative of undercooling show that inclusions were incorporated in their rhyolitic hosts as blobs of magma. Inclusions were probably dispersed throughout small volumes of rhyolitic magma by convective (mechanical) mixing. Inclusion magma was formed by mixing (hybridization) at the interface between basaltic and rhyolitic magmas that coexisted in vertically zoned igneous systems. Relict phenocrysts and the bulk compositions of inclusions suggest that silicic endmembers were less differentiated than erupted high-silica rhyolite. Changes in inferred endmembers of magma mixtures with time suggest that the steepness of chemical gradients near the silicic/mafic interface in the zoned reservoir may have decreased as the system matured, although a high-silica rhyolitic cap persisted. The Coso example is an extreme case of large thermal and compositional contrast between inclusion and host magmas; lesser differences between intermediate composition magmas and inclusions lead to undercooling phenomena that suggest smaller ΔT. Vertical compositional zonation in magma chambers has been documented through study of products of voluminous pyroclastic eruptions. Magmatic inclusions in volcanic rocks provide evidence for compositional zonation and mixing processes in igneous systems when only lava is erupted.

California↗
USGS2001

A metallogenic survey of alkalic rocks of Mt. Somma-Vesuvius volcano

Somma-Vesuvius is an alkaline volcano whose products (pumice, scoria and lava) have alkaline (Na2O+K2O) contents between 6 and 16 wt%, Mg number <50, SiO2 59-47 wt% and MgO 0-7.8 wt% (more than 50% of the samples have a content <2 wt%). Immobile-element ratios (Th/Yb, Ta/Yb, Ce/Yb) indicate a shoshonitic character, while the K2O content (4-10 wt%) is characteristic of ultrapotassic rocks. The behavior of selected metals is discussed by grouping them on the basis of the stratigraphic sequence and differentiating the volcanic activity between plinian and interplinian (Rolandi et al., 1998; Ayuso et al., 1998). This allows observation of the variation within each formation from 25.000y. BP to the last historic eruptive cycle (1631-1944 AD). The main processes to explain the wide distribution of the data presented are fractional crystallization of a mantle-derived magma, magma mixing, and contamination with heterogeneous lower and/or upper crust. Variation diagrams distinguish different behavior for groups of metals: Ag (0.01-0.2 ppm), Mo (1-8.8 ppm), W (1.3-13 ppm), Pb (16-250 ppm), Sb (0.2-2.6 ppm), Sc (0.2-61 ppm), Li (15-140 ppm) and Be (1-31 ppm) increase with increasing differentiation and tend to correlate with the incompatible trace elements (Th, Hf, etc). Cu (10-380 ppm), Au (2-143 ppb), Co (0.7-35.1 ppm) and Fe (1.3-6.2 wt%) decrease towards advanced stage of differentiation. Iron also identifies three magmatic groups. The ratio Fe3+/Fe2+ ranges between 0.2 and 1.8, and Fe2O3/ (Fe2O3+FeO) ranges between 0.2 and 0.8, giving rise to an oxidized environment; exceptions are in the samples belonging to the interplinian formations: I, II, medieval and 1631-1994 AD. Fluorine ranges between 0.1 and 0.4 wt% for the complete Mt. Somma-Vesuvius activity, except for the Ottaviano and Avellino plinian (0.8 wt%) events. Chlorine has a wider range, from 0.1 wt% to 1.6 wt%. Mt Somma-Vesuvius has some features similar to those of mineralized alkaline magmatic systems which coincide with the transition between subduction-related compression and extension-related to continental rifting. We infer that a prospective time for the formation of mineralization at Mt Somma-Vesuvius was during the 1631-1944 eruptive period.

Mineralogy and Petrology↗
USGS1982

Uranium and thorium enrichment in rocks from the base of DSDP Hole 465A, Hess Rise, central North Pacific

Uranium and thorium are concentrated in Cretaceous limestone, chert, ash, basalt, and other rock types at Deep Sea Drilling Project Site 465 located on the southern Hess Rise in the central North Pacific. U concentrations, up to 194 ppm on a carbonate-free basis, are among the highest recorded for any deep-sea deposits. U was initially derived from seawater and concentrated by absorption on terrigenous (humic) organic matter in limestone in a shallow marine environment. U and Th were probably concentrated further by low-temperature hydrothermal fluids emanating from the basaltic basement. Mainly montmorillonite, an alteration product of basalt and ash, and organic matter in sedimentary rocks acted as hosts for U and Th. The unique combination of sediments rich in humic organic matter, abundant smectite in altered ash and basalt, and warm hydrothermal solutions provided the necessary conditions for migration and concentration of U and Th. To better understand the conditions limiting the migrating and concentration of U and Th, other rocks deposited during the ocean-wide Cretaceous anoxic events should be analyzed for these elements. ?? 1982.

Chemical Geology↗
USGS1983

Hydrostratigraphic subdivisions and fault barriers of the Edwards aquifer, south-central Texas, U.S.A.

The karstic Edwards Limestone within the Balcones Fault Zone of south-central Texas forms a productive confined aquifer that consists predominately of dense carbonate rocks and contains several layers of highly permeable and porous honeycombed rocks that have been produced by the leaching of evaporitic, tidal flat or reefal deposits. Fractures have hydraulically interconnected these layers at some places. Faults, however, commonly place rocks of very high-permeability opposite rocks of very low permeability, thus creating a lateral discontinuity and a flow barrier. At places, fault barriers probably cause partial to almost complete blockage of groundwater flow normal to the fault.

Texas↗
USGS1988

Cyclic development of igneous features and their relationship to high-temperature hydrothermal features in the Henderson porphyry molybdenum deposit, Colorado

The Henderson porphyry molybdenum deposit was formed by the superposition of coupled alteration and mineralization events, of varying intensity and size, that were associated with each of at least 11 intrusions. Deposition of molybdenite was accompanied by time-equivalent silicic and potassic alteration. High-temperature alteration and mineralization are spatially and temporally linked to the crystallization of compositionally zoned magma in the apex of stocks. Differences in hydrothermal features associated with each intrusion (e.g., mass of ore, orientation and type of veins, density of veins, and intensity of alteration) correlate with differences in primary igneous features (e.g., composition, texture, morphology, and size). The systematic relations between hydrothermal and magmatic features suggest that primary magma compositions, including volatile contents, largely control the geometry, volume, level of emplacement, and mechanisms of crystallization of stocks. These elements in turn govern the orientations and densities of fractures, which ultimately determine the distribution patterns of hydrothermal alteration and mineralization.Based on primary igneous features, intrusions are grouped into four types, 1 to 4. The first three types define a potassic series of compositions (normarive orthoclase/albite greater than 1) and form a continuum from texturally and compositionally simple intrusions (type 1) to complex intrusions (type 3). Intensity and volume of high-temperature alteration and mineralization associated with a given stock increase from type 1 (2% of total ore) to type 3 (77% of total ore). Complex and strongly mineralizing intrusions (type 3) are separated from one another in time by relatively simple and weakly mineralizing intrusions (type 1). Stocks of type 4, the youngest intrusions, define a sodic series of compositions (normative orthoclase/albite less than 1) and are associated with the waning stages of mineralization.A number of textural features indicate that highly mineralizing type 3 stocks contained high primary concentrations of volatile components, e.g., the presence of unidirectional solidification textures, aplitic rather than aphanitic groundmass, extreme local textural variability, low percentages of phenocrysts in apices, brecciation of apices, and low volumes of dikes. From apex to root zone, textural units within the Seriate stock (type 3), the most productive stock in the deposit, include: (1) a Brain Rock unit with abundant quartz + or - fluorite crenulate layers, (2) a Border unit of generally low but variable phenocryst content (0-25%), (3) a transition zone, 5 to 10 m wide, of unidirectional solidification textures, (4) an Intermediate unit of moderate phenocryst content (25%), (5) another transition zone, 5 to 10 m wide, of unidirectional solidification textures, (6) a Porphyry unit of high phenocryst contents (40%), and (7) a Granite Porphyry or Granite unit. Crystals in layers of unidirectional textures always project toward the interior of the stock and indicate progressive inward solidification of magma along the walls of a chamber. Variations in texture are accompanied by variations in primary composition: the apex of the Seriate stock (the region above the deepest transition zone of unidirectional textures) is enriched in K 2 O and SiO 2 and depleted in Na 2 O, F, Nb, and Y relative to deeper units.Mineralization in the deposit is controlled by moderately outward-dipping concentric veins of both replacement and open-space origin, and by steeply dipping radial veins of replacement origin. Both sets of veins were formed nearly simultaneously about a stock and are focused in a systematic manner on the apex. A classic stockwork of veins occurs only in regions where vein sets associated with spatially separated intrusions overlap. Fluids that filled outward-dipping concentric structures flowed downward and outward from a stock. Fluid pressures in excess of lithostatic pressures, generated during crystallization of magma, were required to open and fill concentric structures. As magma solidified progressively inward, the zone of fluid evolution also migrated downward and inward. With time, the volume of evolved fluids decreased: vein densities decrease from greater than 200/m in the Seriate Brain Rock unit to less than 0.1/m immediately below the last transition zone separating the Seriate Intermediate unit from Seriate Porphyry unit. Crosscutting relations between veins and high-level dikes associated with the Seriate stock establish that most of the ore related to the Seriate stock was deposited prior to solidification of its deepest transition zone of unidirectional solidification textures.The absence of high-temperature veins and associated hydrothermal alteration in deep cores of stocks, the distribution of ore about the high levels of stocks, the orientation of veins about the apex of stocks, and the crosscutting relations between veins and dikes of the same stock are suggestive of initially high concentrations of molybdenum and volatiles in the apex of a stock immediately prior to the onset of significant crystallization. Additional accumulation of ore components, if any, ceased after solidification of the apex. Assignment of molybdenum in the ore shell about the Seriate stock to the volume of solid occupied by the apex of the Seriate stock yields concentration levels in the apical magma of approximately 13,000 ppm Mo.

Economic Geology↗
USGS1953

Monazite deposits of the southeastern Atlantic States

Monazite, a phosphate of the rare earths, is the principal mineral from which the cerium earths and thorium are obtained. Fluviatile monazite placers were mined in the Piedmont province of North and South Carolina from 1887 to 1911, and again intermittently from 1915 to 1917; but the principal sources In recent years have been the beach placers of India and Brazil. In 1946, an embargo was placed on the exportation of Indian monazite, and the Brazilian production has not increased materially to replace this loss. Accordingly monazite in recent years has become a scarce commodity. The principal domestic sources from which monazite may be recovered commercially are in Idaho and in the Piedmont province of the southeastern States. Some monazite is now being produced in Idaho, and a small output is being recovered as a byproduct of heavy mineral mining in Florida. The southeastern placers were not exhausted by the earlier mining and new deposits have been discovered; but production from this region awaits adequate exploration. The country rock of the southeastern Piedmont province is a complex assemblage of metamorphic and igneous rocks. The monazite occurs in two belts. A western belt has been traced from east-central Virginia for 600 miles southwestward into Alabama; and an eastern belt has been traced from the vicinity of Fredericksburg, Va., south-southwestward for 200 miles into North Carolina. Monazite-bearing rocks near. Rion, S. C., appear to indicate a southwestward continuation of the eastern belt. The western, or principal belt, includes the placers that were formerly mined in North and South Carolina. These placers were sampled, and the monazite was separated from the best of the samples, for mineralogical and chemical analysis. The tabulated results show a mean tenor, in the headwater placers of highest grade, of 8.4 pounds of monazite to the cubic yard. Farther downstream where mining must be done to obtain larger yardages, the tenor will be much lower. The mean contents of ThO2 and U3O8 in the placer monazite are shown to be respectively about 5. 7 and 0.4 percents. The western monazite belt was explored northeastward and southwestward from the sites of earlier mining by sampling the weathered bedrock; and the eastern monazite belt was discovered and sampled by the same technique. The principal source-rocks are certain types of granitic intrusives, granitized and pegmatitized country rock, and certain granitic gneisses of the Carolina gneiss. Some of the associated pegmatites also contain high percentages of monazite. Most of the monazite-bearing granitic intrusives are quartz monzonite or closely related rocks. The mean tenor of monazite in bedrock is about 0.006 percent. No search has yet been made for workable placers in these belts beyond the original sites of mining. Monazite derived from bedrock sources in the piedmont has been found in small quantities in all of the Coastal Plain formations, but the tenor is too low to warrant mining for this mineral alone. At favored localities, however, commercial deposits of heavy minerals may be found, similar to those now being mined in Florida, that may yield monazite as a byproduct. Small fluviatile deposits of heavy minerals, including monazite, that were reconcentrated from detrital deposits of Cretaceous age, have recently been found in Georgia and South Carolina, along the inner margin of the Coastal Plain. The monazite belts are conceived to be the sites of early pre-Cambrian valleys, wherein detrital monazite derived from an earlier pre-Cambrian granite, was distributed. These ancient fluviatile deposits were later reconstituted into gneisses of Carolina age, and parts of the latter were remelted to form monazite-bearing granitic intrusives. Some of the monazite-bearing granites may also have originated by the remelting of earlier pre-Cambrian intrusives. The distribution of iron ores in the monazite-bearing rocks appears to accord with

Circular↗
USGS1988

International strategic minerals inventory summary report; titanium

Ilmenite and rutile are currently the most important titanium-bearing minerals, although anatase may be important in the future. Both ilmenite and rutile occur in hard-rock and placer deposits, but at present all rutile production and about half of the ilmenite production are from placer deposits. Anatase occurs in laterite deposits in Brazil, which at present are largely undeveloped. World ilmenite resources in identified deposits that are economically exploitable (R1E} are sufficient for about 150 years at current production rates, and about two-thirds of these resources are in China, the Soviet Union, and Norway. World rutile R1E resources would last about 80 years at current production rates, and some 54 percent of these resources are in Australia, the United States, and Italy. Combined R1E resources of anatase (which are all in Brazil) and rutile would last 300 years at current rutile production rates. Over 95 percent of the world's mine production of titanium-bearing minerals is used to manufacture titanium dioxide pigment for paint and other products. Most of the remaining 4 to 5 percent of production, which is largely rutile, is used for making titanium metal. Australia and Canada are the largest ilmenite producers, together supplying about half the world total; South Africa, Norway, and the Soviet Union together account for another third. Australia accounts for half the total world rutile production, with Sierra Leone and South Africa together accounting for another third. Australia and Norway are the largest exporters of titanium minerals. Unless major new deposits are discovered and developed in the traditional producing countries, the pattern of world production of both ilmenite and rutile could change substantially by 2020.

Circular↗
USGS1989

Mineral occurrence and drill-hole location map of the International Falls 1 degree by 2 degrees quadrangle, Minnesota and Ontario

A project to assess the mineral potential of the U.S. part of the International Fall 1&deg; x 2&deg; quadrangle was undertaken by the U.S. Geological Survey (USGS) in the early 1984, as part of the Conterminous United States Mineral Assessment Program (CUSMAP). Because glacial drift covers most of the basement rocks south of the U.S.-Canada border and mineral production in this part of Minnesota has been virtually nonexistent, data from the adjacent part of Ontario has been used to understand the geologic framework and to evaluate mineral-deposit models relevant to the assessment of the U.S. part of the International Falls quadrangle. This map and accompanying tables show the locations of mineral occurrences, prospects and mines in both Canada and the United States, and summarize their lithologic association and the characteristic metals found in them. Locations of drill holes within the United States and completed before 1987 are also included on the map.

Minnesota, Ontario↗
USGS2010

Geochemical evolution processes and water-quality observations based on results of the National Water-Quality Assessment Program in the San Antonio segment of the Edwards aquifer, Texas, 1996-2006

As part of the National Water-Quality Assessment Program, the U.S. Geological Survey collected and analyzed groundwater samples during 1996-2006 from the San Antonio segment of the Edwards aquifer of central Texas, a productive karst aquifer developed in Cretaceous-age carbonate rocks. These National Water-Quality Assessment Program studies provide an extensive dataset of groundwater geochemistry and water quality, consisting of 249 groundwater samples collected from 136 sites (wells and springs), including (1) wells completed in the shallow, unconfined, and urbanized part of the aquifer in the vicinity of San Antonio (shallow/urban unconfined category), (2) wells completed in the unconfined (outcrop area) part of the regional aquifer (unconfined category), and (3) wells completed in and springs discharging from the confined part of the regional aquifer (confined category). This report evaluates these data to assess geochemical evolution processes, including local- and regional-scale processes controlling groundwater geochemistry, and to make water-quality observations pertaining to sources and distribution of natural constituents and anthropogenic contaminants, the relation between geochemistry and hydrologic conditions, and groundwater age tracers and travel time. Implications for monitoring water-quality trends in karst are also discussed. Geochemical and isotopic data are useful tracers of recharge, groundwater flow, fluid mixing, and water-rock interaction processes that affect water quality. Sources of dissolved constituents to Edwards aquifer groundwater include dissolution of and geochemical interaction with overlying soils and calcite and dolomite minerals that compose the aquifer. Geochemical tracers such as magnesium to calcium and strontium to calcium ratios and strontium isotope compositions are used to evaluate and constrain progressive fluid-evolution processes. Molar ratios of magnesium to calcium and strontium to calcium in groundwater typically increase along flow paths; results for samples of Edwards aquifer groundwater show an increase from shallow/urban unconfined, to unconfined, to confined groundwater categories. These differences are consistent with longer residence times and greater extents of water-rock interaction controlling fluid compositions as groundwater evolves from shallow unconfined groundwater to deeper confined groundwater. Results for stable isotopes of hydrogen and oxygen indicate specific geochemical processes affect some groundwater samples, including mixing with downdip saline water, mixing with recent recharge associated with tropical cyclonic storms, or mixing with recharge water than has undergone evaporation. The composition of surface water recharging the aquifer, as well as mixing with downdip water from the Trinity aquifer or the saline zone, also might affect water quality. A time-series record (1938-2006) of discharge at Comal Springs, one of the major aquifer discharge points, indicates an upward trend for nitrate and chloride concentrations, which likely reflects anthropogenic activities. A small number of organic contaminants were routinely or frequently detected in Edwards aquifer groundwater samples. These were the pesticides atrazine, its degradate deethylatrazine, and simazine; the drinking-water disinfection byproduct chloroform; and the solvent tetrachloroethene. Detection of these contaminants was most frequent in samples of the shallow/urban unconfined groundwater category and least frequent in samples of the unconfined groundwater category. Results indicate that the shallow/urban unconfined part of the aquifer is most affected by anthropogenic contaminants and the unconfined part of the aquifer is the least affected. The high frequency of detection for these anthropogenic contaminants aquifer-wide and in samples of deep, confined groundwater indicates that the entire aquifer is susceptible to water-quality changes as a result of anthropogenic activities. L

Texas↗
USGS2011

Sedimentation and occurrence and trends of selected nutrients, other chemical constituents, and cyanobacteria in bottom sediment, Clinton Lake, northeast Kansas, 1977-2009

A combination of available bathymetric-survey information and bottom-sediment coring was used to investigate sedimentation and the occurrence of selected nutrients (total nitrogen and total phosphorus), organic and total carbon, 25 trace elements, cyanobacterial akinetes, and the radionuclide cesium-137 in the bottom sediment of Clinton Lake, northeast Kansas. The total estimated volume and mass of bottom sediment deposited from 1977 through 2009 in the conservation (multi-purpose) pool of the reservoir was 438 million cubic feet and 18 billion pounds, respectively. The estimated sediment volume occupied about 8 percent of the conservation-pool, water-storage capacity of the reservoir. Sedimentation in the conservation pool has occurred about 70 percent faster than originally projected at the time the reservoir was completed. Water-storage capacity in the conservation pool has been lost to sedimentation at a rate of about 0.25 percent annually. Mean annual net sediment deposition since 1977 in the conservation pool of the reservoir was estimated to be 563 million pounds per year. Mean annual net sediment yield from the Clinton Lake Basin was estimated to be 1.5 million pounds per square mile per year. Typically, the bottom sediment sampled in Clinton Lake was at least 99 percent silt and clay. The mean annual net loads of total nitrogen and total phosphorus deposited in the bottom sediment of Clinton Lake were estimated to be 1.29 million pounds per year and 556,000 pounds per year, respectively. The estimated mean annual net yields of total nitrogen and total phosphorus from the Clinton Lake Basin were 3,510 pounds per square mile per year and 1,510 pounds per square mile per year, respectively. Throughout the history of Clinton Lake, total nitrogen concentrations in the deposited sediment generally were uniform and indicated consistent inputs to the reservoir over time. Likewise, total phosphorus concentrations in the deposited sediment generally were uniform. Although, for two of three coring sites, a possible positive trend in phosphorus deposition was indicated. The Wakarusa River possibly was a larger contributor of nitrogen and phosphorus to Clinton Lake than was Rock Creek. As a principal limiting factor for primary production in most freshwater environments, phosphorus is of particular importance because increased inputs can contribute to accelerated reservoir eutrophication and the production of algal toxins and taste-and-odor compounds. Trace-element concentrations in the bottom sediment of Clinton Lake generally were uniform over time. As is typical for eastern Kansas reservoirs, arsenic, chromium, and nickel concentrations typically exceeded the threshold-effects guidelines, which represent the concentrations above which toxic biological effects occasionally occur. Zinc concentrations frequently exceeded the threshold-effects guideline. Trace-element concentrations did not exceed the probable-effects guidelines (available for eight trace elements), which represent the concentrations above which toxic biological effects usually or frequently occur. Cyanobacterial akinetes (cyanobacteria resting stage) in the bottom sediment of Clinton Lake, combined with historical water-quality data on chlorophyll-a and total phosphorus concentrations, indicated that the reservoir likely has been eutrophic throughout most of its history. A statistically significant increase in cyanobacterial akinetes in the bottom sediment indicated that Clinton Lake may have become more eutrophic over the life of the reservoir. The increase in cyanobacterial akinetes may, in part, be related to a possible increase in total phosphorus concentrations.

Scientific Investigations Report↗
USGS1996

Evaluation of agricultural best-management practices in the Conestoga River headwaters, Pennsylvania: Effects of nutrient management on water quality in the Little Conestoga Creek headwaters, 1983-89

Water quality in the headwaters of the Little Conestoga Creek, Lancaster County, Pa., was investigated from April 1986 through September 1989 to determine possible effects of agricultural nutrient management on water quality. Nutrient management, an agricultural Best-Management Practice, was promoted in the 5.8-square-mile watershed by the U.S. Department of Agriculture Rural Clean Water Program. Nonpoint-source- agricultural contamination was evident in surface water and ground water in the watershed; the greatest contamination was in areas underlain by carbonate rock and with intensive row-crop and animal production. Initial implementation of nutrient management covered about 30 percent of applicable land and was concentrated in the Nutrient-Management Subbasin. By 1989, nutrient management covered about 45 percent of the entire Small Watershed, about 85 percent of the Nutrient- Management Subbasin, and less than 10 percent of the Nonnutrient-Management Subbasin. The number of farms implementing nutrient management increased from 14 in 1986 to 25 by 1989. Nutrient applications to cropland in the Nutrient- Management Subbasin decreased by an average of 35 percent after implementation. Comparison of base- flow surface-water quality from before and after implementation suggests that nutrient management was effective in slowing or reversing increases in concentrations of dissolved nitrate plus nitrite in the Nutrient-Management Subbasin. Although not statistically significant, the Mann-Whitney step-trend coefficient for the Nutrient-Management Subbasin was 0.8 milligram per liter, whereas trend coefficients for the Nonnutrient-Management Subbasin and the Small Watershed were 0.4 and 1.4 milligrams per liter, respectively, for the period of study. Analysis of covariance comparison of concurrent concentrations from the two sub- basins showed a significant decrease in concen- trations from the Nutrient-Management Subbasin compared to the Nonnutrient-Management Subbasin. The small, positive effect of nutrient management on base-flow water quality should be interpreted with caution. Lack of statistical significance for most tests, short-term variation in climate and agricultural activities, unknown ground-water flow rates, and insufficient agricultural-activity data for farms outside of the Nutrient-Management Subbasin were potential problems. A regression model relating nutrient applications to concen- trations of dissolved nitrate plus nitrite showed no significant explanatory relation.

Pennsylvania↗
USGS2002

Detection and mapping of fractures and cavities using borehole radar

Borehole radar can be used in a single-hole reflection mode or in a cross-hole tomography mode. In the reflection mode, radar provides an image of discontinuities in the bedrock surrounding a borehole, including bedding planes, lithologic contacts, fractures, and cavities. The measurements are either directional or omni-directional, depending upon the type of equipment and antennas. In the tomography mode, where the transmitter and receiver are in separate boreholes, radar provides an image of the planar section between the boreholes. The radius of investigation depends on the antenna frequency and the electrical conductivity of the bedrock. For a central frequency of 100 megahertz, in the reflection mode the ranges are typically 10 to 40 meters in resistive solid rock and less than 5 meters in conductive, clay-rich, or silty rock. Single-hole and cross-hole radar also have been used for water-supply investigations in the northeast-ern United States. Borehole radar was used to investigate crystalline bedrock in two rapidly developing com-munities that rely on water resources in the bedrock. The surveys were conducted and interpreted along with data from other borehole geophysical tools. The borehole radar surveys were used to identify the location and orientation of reflectors, locate the primary pathways of flow to the supply wells, and identify aquifer character-istics that may be useful in siting a production well and protecting high-yielding wells in crystalline rocks. Borehole radar has been used to investigate fractures, cavities, and lithologic changes at several sites in Europe. The radar data has been interpreted in conjuction with the results of modeling of borehole-radar re-sponse. At the Grimsel nuclear waste laboratory in Switzerland, single-hole reflection and tomography methods were used to characterize the rock in inclined boreholes. At numerous geotechnical sites in Belgium, France, and the Netherlands, borehole radar has been used to characterize the rock and identify fractures and cavities.

Conference Paper↗
USGS2001

The Putumayo-Oriente-Maranon Province of Colombia, Ecuador, and Peru; Mesozoic-Cenozoic and Paleozoic petroleum systems

This report is an evaluation of oil and gas resources for petroleum systems of the Putumayo-Oriente-Maranon province of Columbia, Ecuador, and Peru. This assessment is a product of the World Energy Project of the U.S. Geological Survey, under the direction of Thomas Ahlbrandt. Described in this explanation of the petroleum geology of the Putumayo-Oriente-Maranon province are thermal maturation of hydrocarbon source rocks, primary reservoir formations, areas and volumes of oil and (or) gas production, and the history of exploration. Complete oil and gas resource assessment results are planned for a later publication, although some data and results are contained in this report.

Data Series↗
USGS1996

Summary of the Oahu, Hawaii, regional aquifer-system analysis

Oahu, the third largest of the Hawaiian islands, is formed by the eroded remnants of two elongated shield volcanoes with broad, low profiles. Weathering and erosion have modified the original domed surfaces of the volcanoes, leaving a landscape of deep valleys and steep interfluvial ridges in the interior highlands. The Koolau Range in eastern Oahu and the Waianae Range in western Oahu are the eroded remnants of the Koolau and Waianae Volcanoes. The origin, mode of emplacement, texture, and composition of the rocks of Oahu affect their ability to store and transmit water. The volcanic rocks are divided into four groups: (1) lava flows, (2) dikes, (3) pyroclastic deposits, and (4) saprolite and weathered basalt. Stratified sequences of thin-bedded lava flows form the most productive aquifers in Hawaii. Dikes are near-vertical sheets of massive intrusive rock that typically contain only fracture permeability. Pyroclastic deposits include ash, cinder, and spatter; they are essentially granular, with porosity and permeability similar to those of granular sediments. Weathering of basaltic rocks in the humid, subtropical climate of Oahu alters igneous minerals to clays and oxides, reducing the permeability of the parent rock. Saprolite is weathered material that has retained textural features of the parent rock. Estimates of hydraulic conductivity along the plane of dike-free lava flows tend to fall within about one order of magnitude, from about 500 to about 5,000 feet per day. Estimates of specific yield range from about 1 to 20 percent; most of the values lie within a narrow range of about 5 to 10 percent. The occurrence of ground water on Oahu is determined by the type and character of the rocks and by the presence of geohydrologic barriers. The primary modes of freshwater occurrence on Oahu are as a basal lens of fresh ground water floating on saltwater, as dike-impounded ground water, and as perched ground water. Saltwater occurs at depth throughout much of the island. A regional aquifer system composed of the Waianae aquifer in the Waianae Volcanics and the Koolau aquifer in the Koolau Basalt is subdivided into well-defined areas by geohydrologic barriers. The aquifers are separated by the Waianae confining unit formed by weathering along the Waianae-Koolau unconformity. In some coastal areas, a caprock of sedimentary deposits overlies and confines the aquifers. The island of Oahu has been divided into seven major ground-water areas delineated by deep-seated structural geohydrologic barriers; these areas are further subdivided by shallower internal barriers to ground-water flow. The Koolau rift zone along the eastern (windward) side of the island and the Waianae rift zone to the west (Waianae area) constitute two of the major ground-water areas. North-central Oahu is divided into three smaller ground-water areas, Mokuleia, Waialua, and Kawailoa. The Schofield ground-water area encompasses much of the Schofield Plateau of central Oahu. Southern Oahu is divided into six areas, Ewa, Pearl Harbor, Moanalua, Kalihi, Beretania, and Kaimuki. Southeastern Oahu is divided into the Waialae and Wailupe-Hawaii Kai areas. Along the northeast coast of windward Oahu is the Kahuku ground-water area. The aquifers of Oahu contain shallow freshwater and deeper saltwater flow systems. There are five fresh ground-water flow systems: meteoric freshwater flow diverges from ground-water divides that lie somewhere within the Waianae and Koolau rift zones, forming an interior flow system in central Oahu (which is divided into the northern and southern Oahu flow systems) and exterior flow systems in western (Waianae area) Oahu, eastern (windward) Oahu, and southeastern Oahu. Development of the ground-water resources on Oahu began when the first well was drilled near Honouliuli in the summer of 1879. By 1890, 86 wells had been drilled on the island. From about 1891 to about 1910, development increased rapidly with the drilling of a

Hawaii↗
USGS2022

Pore systems and organic petrology of cretaceous Mowry and Niobrara source-rock reservoirs, Powder River Basin, Wyoming, USA

The Powder River Basin (PRB) is a world-class oil province, in large part thanks to contributions from premier source rocks, Cretaceous Mowry and Niobrara shales. Both formations are also unconventional reservoirs. A critical aspect of evaluating production potential and finding sweet spots is the nature of the pore systems in these fine-grained source-rock reservoirs. Variation by stratigraphic interval is important for selecting optimum target zones for horizontal wells. Understanding variation in pore type, size, and connectivity and relationships with mineralogy and fabric help in determining prospectivity in different parts of the basin. Deciphering controls on pore-system development helps predict intervals and locations of optimum reservoir quality. Imaging of Niobrara and Mowry samples from a range of thermal maturities provided observations and data on pore systems, organic matter (OM) types and associations with mineralogy and fabric, wettability, and microporosity associated with both diagenetic and detrital clays. Imaging techniques included scanning electron microscopy, organic petrography and correlative scanning electron microscopy, and mapping of mineralogy through energy dispersive spectroscopy. Mean solid bitumen (BR o ) and vitrinite reflectance (VR o ) values indicate all samples are in the oil window with values ranging from 0.52 to 1.15%. Organic fluorescence is prominent in amorphous OM, solid bitumen and some vitrinite in the early oil window. The fluorescence is extinguished at higher thermal maturity. Carbonate pellets (in Niobrara) mainly contain migrated solid bitumen and residual live oil and little or no terrigenous OM (vitrinite and inertinite). However, terrigenous OM is common in siliceous/argillaceous laminae in both formations, where it occurs with amorphous OM, some of which has converted in situ to a solid bitumen petroleum residue. One key finding is the widespread presence of migrated OM at very early oil window maturity. Distribution of such OM and associated wettability alteration is fabric-controlled, at all levels of thermal maturity studied. Clay morphology and abundance and supporting rigid mineral grain framework strongly influence pore development, preservation, and connectivity in both formations. Carbonate content is a good proxy for reservoir quality in Niobrara intervals due to association of porous solid bitumen with calcareous fecal pellets. High recrystallized microquartz content is associated with the best reservoir intervals in the Mowry.

Wyoming↗
USGS2009

Methods for Estimating Water Withdrawals for Mining in the United States, 2005

The mining water-use category includes groundwater and surface water that is withdrawn and used for nonfuels and fuels mining. Nonfuels mining includes the extraction of ores, stone, sand, and gravel. Fuels mining includes the extraction of coal, petroleum, and natural gas. Water is used for mineral extraction, quarrying, milling, and other operations directly associated with mining activities. For petroleum and natural gas extraction, water often is injected for secondary oil or gas recovery. Estimates of water withdrawals for mining are needed for water planning and management. This report documents methods used to estimate withdrawals of fresh and saline groundwater and surface water for mining during 2005 for each county and county equivalent in the United States, Puerto Rico, and the U.S. Virgin Islands. Fresh and saline groundwater and surface-water withdrawals during 2005 for nonfuels- and coal-mining operations in each county or county equivalent in the United States, Puerto Rico, and the U.S. Virgin Islands were estimated. Fresh and saline groundwater withdrawals for oil and gas operations in counties of six states also were estimated. Water withdrawals for nonfuels and coal mining were estimated by using mine-production data and water-use coefficients. Production data for nonfuels mining included the mine location and weight (in metric tons) of crude ore, rock, or mineral produced at each mine in the United States, Puerto Rico, and the U.S. Virgin Islands during 2004. Production data for coal mining included the weight, in metric tons, of coal produced in each county or county equivalent during 2004. Water-use coefficients for mined commodities were compiled from various sources including published reports and written communications from U.S. Geological Survey National Water-use Information Program (NWUIP) personnel in several states. Water withdrawals for oil and gas extraction were estimated for six States including California, Colorado, Louisiana, New Mexico, Texas, and Wyoming, by using data from State agencies that regulate oil and gas extraction. Total water withdrawals for mining in a county were estimated by summing estimated water withdrawals for nonfuels mining, coal mining, and oil and gas extraction. The results of this study were distributed to NWUIP personnel in each State during 2007. NWUIP personnel were required to submit estimated withdrawals for numerous categories of use in their States to a national compilation team for inclusion in a national report describing water use in the United States during 2005. NWUIP personnel had the option of submitting the estimates determined by using the methods described in this report, a modified version of these estimates, or their own set of estimates or reported data. Estimated withdrawals resulting from the methods described in this report may not be included in the national report; therefore the estimates are not presented herein in order to avoid potential inconsistencies with the national report. Water-use coefficients for specific minerals also are not presented to avoid potential disclosure of confidential production data provided by mining operations to the U.S. Geological Survey.

Scientific Investigations Report↗