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G.S. Plumlee

Publications and source records attributed to G.S. Plumlee.

At least 19 recordsLinked to original sources
USGS2014

Asphaltene content and composition as a measure of Deepwater Horizon oil spill losses within the first 80 days

The composition and content of asphaltenes in spilled and original wellhead oils from the Deepwater Horizon (DWH) incident provide information on the amount of original oil lost and the processes most responsible for the losses within the first 80 days of the active spill. Spilled oils were collected from open waters, coastal waters and coastal sediments during the incident. Asphaltenes are the most refractory component of crude oils but their alteration in the spilled oils during weathering prevents them from being used directly as a conservative component to calculate original oil losses. The alteration is reflected by their increase in oxygen content and depletion in 12 C. Reconnaissance experiments involving evaporation, photo-oxidation, microbial degradation, dissolution, dispersion and burning indicate that the combined effects of photo-oxidation and evaporation are responsible for these compositional changes. Based on measured losses and altered asphaltenes from these experiments, a mean of 61 ± 3 vol% of the original oil was lost from the surface spilled oils during the incident. This mean percentage of original oil loss is considerably larger than previous estimates of evaporative losses based on only gas chromatography (GC) amenable hydrocarbons (32–50 vol%), and highlights the importance of using asphaltenes, as well as GC amenable parameters in evaluating original oil losses and the processes responsible for the losses.

Gulf Of Mexico↗
USGS2011

Simultaneous speciation of arsenic, selenium, and chromium: species, stability, sample preservation, and analysis of ash and soil leachates

An analytical method using high-performance liquid chromatography separation with inductively coupled plasma mass spectrometry (ICP-MS) detection previously developed for the determination of Cr(III) and Cr(VI) has been adapted to allow the determination of As(III), As(V), Se(IV), Se(VI), Cr(III), and Cr(VI) under the same chromatographic conditions. Using this method, all six inorganic species can be determined in less than 3 min. A dynamic reaction cell (DRC)-ICP-MS system was used to detect the species eluted from the chromatographic column in order to reduce interferences. A variety of reaction cell gases and conditions may be utilized with the DRC-ICP-MS, and final selection of conditions is determined by data quality objectives. Results indicated all starting standards, reagents, and sample vials should be thoroughly tested for contamination. Tests on species stability indicated that refrigeration at 10° C was preferential to freezing for most species, particularly when all species were present, and that sample solutions and extracts should be analyzed as soon as possible to eliminate species instability and interconversion effects. A variety of environmental and geological samples, including waters and deionized water [leachates] and simulated biological leachates from soils and wildfire ashes have been analyzed using this method. Analytical spikes performed on each sample were used to evaluate data quality. Speciation analyses were conducted on deionized water leachates and simulated lung fluid leachates of ash and soils impacted by wildfires. These results show that, for leachates containing high levels of total Cr, the majority of the chromium was present in the hexavalent Cr(VI) form. In general, total and hexavalent chromium levels for samples taken from burned residential areas were higher than those obtained from non-residential forested areas. Arsenic, when found, was generally in the more oxidized As(V) form. Selenium (IV) and (VI) were present, but typically at low levels.

Analytical and Bioanalytical Chemistry↗
USGS2009

Naturally acidic surface and ground waters draining porphyry-related mineralized areas of the Southern Rocky Mountains, Colorado and New Mexico

Acidic, metal-rich waters produced by the oxidative weathering and resulting leaching of major and trace elements from pyritic rocks can adversely affect water quality in receiving streams and riparian ecosystems. Five study areas in the southern Rocky Mountains with naturally acidic waters associated with porphyry mineralization were studied to document variations in water chemistry and processes that control the chemical variations. Study areas include the Upper Animas River watershed, East Alpine Gulch, Mount Emmons, and Handcart Gulch in Colorado and the Red River in New Mexico. Although host-rock lithologies in all these areas range from Precambrian gneisses to Cretaceous sedimentary units to Tertiary volcanic complexes, the mineralization is Tertiary in age and associated with intermediate to felsic composition, porphyritic plutons. Pyrite is ubiquitous, ranging from ???1 to >5 vol.%. Springs and headwater streams have pH values as low as 2.6, SO4 up to 3700 mg/L and high dissolved metal concentrations (for example: Fe up to 400 mg/L; Cu up to 3.5 mg/L; and Zn up to 14.4 mg/L). Intensity of hydrothermal alteration and presence of sulfides are the primary controls of water chemistry of these naturally acidic waters. Subbasins underlain by intensely hydrothermally altered lithologies are poorly vegetated and quite susceptible to storm-induced surface runoff. Within the Red River study area, results from a storm runoff study documented downstream changes in river chemistry: pH decreased from 7.80 to 4.83, alkalinity decreased from 49.4 to <1 mg/L, SO4 increased from 162 to 314 mg/L, dissolved Fe increased from to 0.011 to 0.596 mg/L, and dissolved Zn increased from 0.056 to 0.607 mg/L. Compared to mine drainage in the same study areas, the chemistry of naturally acidic waters tends to overlap but not reach the extreme concentrations of metals and acidity as some mine waters. The chemistry of waters draining these mineralized but unmined areas can be used to estimate premining conditions at sites with similar geologic and hydrologic conditions. For example, the US Geological Survey was asked to estimate premining ground-water chemistry at the Questa Mo mine, and the proximal analog approach was used because a mineralized but unmined area was located adjacent to the mine property. By comparing and contrasting water chemistry from different porphyry mineralized areas, this study not only documents the range in concentrations of constituents of interest but also provides insight into the primary controls of water chemistry.

Applied Geochemistry↗
USGS2009

Application of in vitro extraction studies to evaluate element bioaccessibility in soils from a transect across the United States and Canada

In vitro bioaccessibility tests (IVBA) are inexpensive, physiologically-based extraction tests designed to estimate the bioaccessibility of elements along ingestion exposure pathways. Published IVBA protocols call for the testing to be done on the <250-??m fraction of soil, as these particles are most likely to adhere to the hands of children and be ingested. Most IVBA in the literature to date have been applied to soil samples from highly contaminated sites or to spiked samples, and relatively little work has been done to evaluate bioaccessibility of elements in a wide variety of uncontaminated 'background' soils. In 2004, the US Geological Survey and the Geological Survey of Canada sampled soils along north-south and east-west transects across the two countries to test and refine sampling and analytical protocols recommended for the planned soil geochemical survey of North America. Samples were collected at 220 sites selected randomly at approximately 40-km intervals. The focus of the investigation presented in this paper was twofold: (1) to begin to examine variations in bioaccessibility of As, Cd, Cr, Ni and Pb in a number of 'background' (i.e., unpolluted) soils from around North America and (2) to determine if there are significant differences that would preclude using the standard size fraction of <2 mm for extraction with a simulated gastric fluid as an expeditious and inexpensive bioaccessibility screening tool for the large numbers of future samples to be collected by this continental-scale project. A subset of 20 soil samples collected along the north-south transect at a depth of 0-5 cm was used for this study. Two separate size fractions (<2 mm and <250 ??m) were extracted using a simulated human gastric fluid consisting of a solution of HCl and glycine adjusted to a pH of 1.5. In general, the leachate results for the <2-mm size fraction were not substantially different than those for the <250-??m size fraction for concentrations of As, Cd, Cr, Ni and Pb. Leachate concentrations for Cd, Ni and Pb appear to be controlled to some extent by the total concentration of the element in soil. Bioaccessibility of the elements in this study decreased in the order, Cd > Pb > Ni > As > Cr.

Applied Geochemistry↗
USGS1994

Fluid chemistry evolution and mineral deposition in the main-stage Creede epithermal system

This paper presents results of chemical speciation and reaction path calculations that model fluid chemistry evolution and ore deposition in the main-stage Creede, Colorado, epithermal system. An extensive geologic, mineralogic, and geochemical framework for mineralization has been developed by many researchers for the central and southern district vein systems (OH and P veins; central and southern Amethyst and Bulldog Mountain vein systems) and is used to constrain and guide the modeling presented in this paper. Previous studies have shown that the central base metal sulfide-rich and southern barite- and silver-rich Creede ores were deposited by hydrothermal brines with temperatures as high as 285 degrees C and salinities as high as 13 wt percent NaCl equiv. Fluid inclusion studies indicate that mixing with dilute steam-heated ground waters was the dominant ore deposition mechanism, although boiling did occur during some stages. Speciation calculations confirm that the hydrothermal fluids, due to their high salinities, were relatively acidic (pH near 5.5) and transported significant quantities of base metals (i.e., up to 10-2 m total concentrations of Zn) as chloride complexes. Reaction path calculations show that strong north-south mineralogical variations in main-stage mineralization are best accounted for by variable boiling of the hydrothermal brines, followed by lateral mixing of the brines with overlying dilute, steam-heated ground waters. The extent of boiling prior to mixing was a function of the temperature and gas contents of the hydrothermal fluids as they first entered the district ore zones from depth, and of the thickness of the steam-heated ground-water column overlying the hydrothermal fluids. The calculations indicate that limited amounts of boiling (during stages when the overlying ground-water column was relatively thick) produced a chlorite-pyrite-hematite-sphalerite-galena-chalcopyrite + or - adularia assemblage in the central district vein systems (OH and P veins; central Amethyst and Bulldog Mountain vein systems). More extensive boiling (during a stage in which the ground-water table apparently dropped considerably) deposited quartz, fluorite, adularia, and hematite with only minor sulfides in the central district veins. Boiling ceased when the saturation pressure of the hydrothermal fluids dropped below hydrostatic pressures generated by the overlying ground-water column. Following boiling, lateral mixing with overlying steam-heated ground waters initially produced sphalerite- and galena-rich assemblages in the central district vein systems. With continued mixing to the south, the hydrothermal fluids deposited abundant barite, subordinate sphalerite, galena, and quartz, and lesser native silver, acanthite, and sulfosalts in the district's southern vein systems (southern Amethyst, southern Bulldog Mountain vein systems).Modeling results for Creede and other epithermal fluid compositions show that epithermal ore grades, mineral assemblages, and mineral zoning patterns are strongly influenced by shallow hydrologic processes such as boiling and fluid mixing. As a result, epithermal mineral assemblages and zoning patterns can be used to reconstruct the paleohydrology of the hydrothermal systems from which they were deposited, and thus provide useful tools for epithermal ore exploration.

Economic Geology↗
USGS1994

Chemical reaction path modeling of ore deposition in Mississippi Valley-type Pb-Zn deposits of the Ozark region, US midcontinent

The Ozark region of the U.S. midcontinent is host to a number of Mississippi Valley-type districts, including the world-class Viburnum Trend, Old Lead Belt, and Tri-State districts and the smaller Southeast Missouri barite, Northern Arkansas, and Central Missouri districts. There is increasing evidence that the Ozark Mississippi Valley-type districts formed locally within a large, interconnected hydrothermal system that also produced broad fringing areas of trace mineralization, extensive subtle hydrothermal alteration, broad thermal anomalies, and regional deposition of hydrothermal dolomite cement. The fluid drive was provided by gravity flow accompanying uplift of foreland thrust belts during the Late Pennsylvanian to Early Permian Ouaehita orogeny.In this study, we use chemical speciation and reaction path calculations, based on quantitative chemical analyses of fluid inclusions, to constrain likely hydrothermal brine compositions and to determine which precipitation mechanisms are consistent with the hydrothermal mineral assemblages observed regionally and locally within each Mississippi Valley-type district in the Ozark region. Deposition of the regional hydrothermal dolomite cement with trace sulfides likely occurred in response to near-isothermal effervescence of CO 2 from basinal brines as they migrated to shallower crustal levels and lower confining pressures. In contrast, our calculations indicate that no one depositional process can reproduce the mineral assemblages and proportions of minerals observed in each Ozark ore district; rather, individual districts require specific depositional mechanisms that reflect the local host-rock composition, structural setting, and hydrology.Both the Northern Arkansas and Tri-State districts are localized by normal faults that likely allowed brines to rise from deeper Cambrian-Ordovician dolostone aquifers into shallower carbonate sequences dominated by limestones. In the Northern Arkansas district, jasperoid preferentially replaced limestones in the mixed dolostone-limestone sedimentary packages. Modeling results indicate that the ore and alteration assemblages in the Tri-State and Northern Arkansas districts resulted from the flow of initially dolomite-saturated brines into cooler limestones. Adjacent to fluid conduits where water/rock ratios were the highest, the limestone was replaced by dolomite. As the fluids moved outward into cooler limestone, jasperoid and sulfide replaced limestone. Isothermal boiling of the ore fluids may have produced open-space filling of hydrothermal dolomite with minor sulfides in breccia and fault zones. Local mixing of the regional brine with locally derived sulfur undoubtedly played a role in the development of sulfide-rich ore runs.Sulfide ores of the Central Missouri district are largely open-space filling of sphalerite plus minor galena in dolostone karst features localized along a broad anticline. Hydrothermal solution collapse during ore deposition was a minor process, indicating dolomite was slightly undersaturated during ore deposition. No silicification and only minor hydrothermal dolomite is present in the ore deposits. The reaction path that best explains the features of the Central Missouri sulfide deposits is the near-isothermal mixing of two dolomite-saturated fluids with different H 2 S and metal contents. Paleokarst features may have allowed the regional brine to rise stratigraphically and mix with locally derived, H 2 S-rich fluids. The Viburnum Trend and Old Lead Belt ores are galena rich with lesser amounts of sphalerite; they replace the most permeable dolostone facies in the Bonneterre Dolomite. Hydrothermal dissolution of host dolostone was concurrent with sulfide deposition, but dolomite deposition occurred episodically between periods of sulfide deposition. The important ore controls in these districts are a variety of sedimentary and geologic features that allowed cross-stratigraphic fluid flow and provided opportunities for fluid mixing. The reaction path which best reproduces the broad features of the Viburnum Trend and Old Lead Belt ores is one in which a dolomite-saturated, lead-rich, zinc- and H 2 S-poor brine mixes with a less saline, H 2 S-rich fluid. The brine became enriched in K, Mg, and Pb and depleted in H 2 S as it flowed through sandstone and redbed aquifers prior to entering the district. This mixing model is consistent with the abundant fluid inclusion and stable isotope evidence for fluid mixing in the districts. Small amounts of cooling associated with the mixing may have contributed to sulfide deposition.

Alabama, Arkansas, Illinois, Indiana, Kansas, Kent↗
USGS1991

Origin of late dolomite cement by CO2-saturated deep basin brines: evidence from the Ozark region, central United States

Studies of fluid inclusions in regionally extensive late dolomite cement (LDC) throughout the Ozark region show that CO 2 effervescence was widespread during dolomite precipitation. On the basis of quantitative analyses of inclusion fluids, reaction-path modeling shows that LDC with trace amounts of sulfides can be deposited by effervescence of a CO 2 -saturated basin brine as it migrates to shallower levels and lower confining pressures. This precipitation mechanism best explains occurrences of LDC in the Ozark region and may account for LDC found in sedimentary basins worldwide.

Geology↗