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Federal Heights, CO, United States

Depine M.,University of Wurzburg | Frimmel H.E.,University of Wurzburg | Frimmel H.E.,University of Cape Town | Emsbo P.,Federal Center | And 2 more authors.
Mineralium Deposita | Year: 2013

The first systematic analyses of the trace and rare earth element (REE) distribution in uraninite from various gold-bearing conglomerates of the Mesoarchaean Central Rand Group in South Africa's Witwatersrand Basin by in situ laser ablation-inductively coupled plasma-mass spectrometry confirms a placer origin for the uraninite and a magmatogenic provenance thereof. The chemistry of commonly rounded to sub-rounded uraninite is highly variable from grain to grain but generally marked by elevated Th, W, Bi, Mo, Ta, Y, REE contents and unusually high Au concentrations. Especially, the high Th contents and the chondrite-normalised REE patterns are incompatible with post-sedimentary hydrothermal genetic models for the U mineralisation and point to derivation of the detrital uraninite from a high-temperature, magmatogenic, presumably granitic to pegmatitic source. The elevated Au concentrations (of as much as 67 ppm) in this uraninite are unique to the Witwatersrand and hint at a granitic hinterland that was enriched in both U and Au, thus presenting a potential source domain for some of the detrital gold in the Witwatersrand conglomerates. Minute fracture fills of brannerite in close proximity to the larger, rounded uraninite grains are devoid of detectable Bi, Mo, REE and Au and have only very low concentrations of Th, W, Ta and Y. This is explicable by crystallisation from a low-temperature hydrothermal fluid. Thus, Witwatersrand U phases show, analogous to many other ore constituents, such as pyrite and gold, clear evidence of partial, short-range mobilisation of originally detrital particles by post-sedimentary fluids. © 2013 Springer-Verlag Berlin Heidelberg. Source

Clow D.W.,U.S. Geological Survey | Clow D.W.,Federal Center | Peavler R.S.,GSIWater Solutions Inc. | Roche J.,National Park Service | And 3 more authors.
Environmental Monitoring and Assessment | Year: 2011

There is concern that visitor-use associated activities, such as bathing, dish washing, wastewater production, and stock animal use near lakes and streams, could cause degradation of water quality in Yosemite National Park. A study was conducted during 2004-2007 to assess patterns in nutrient and Escherichia coli (E. coli) concentrations in the Merced and Tuolumne Rivers and characterize natural background concentrations of nutrients in the park. Results indicated that nutrient and E. coli concentrations were low, even compared to other undeveloped sites in the United States. A multiple linear regression approach was used to model natural background concentrations of nutrients, with basin characteristics as explanatory variables. Modeled nitrogen concentrations increased with elevation, and modeled phosphorus concentrations increased with basin size. Observed concentrations (±uncertainty) were compared to modeled concentrations (±uncertainty) to identify sites that might be impacted by point sources of nutrients, as indicated by large model residuals. Statistically significant differences in observed and modeled concentrations were observed at only a few locations, indicating that most sites were representative of natural background conditions. The empirical modeling approach used in this study can be used to estimate natural background conditions at any point along a study reach in areas minimally impacted by development, and may be useful for setting water-quality standards in many national parks. © 2011 Springer Science+Business Media B.V. (outside the USA). Source

Wieclaw D.,AGH University of Science and Technology | Lewan M.D.,Federal Center | Kotarba M.J.,AGH University of Science and Technology
Geological Quarterly | Year: 2010

Determining kinetic parameters for oil generation from a source rock by hydrous pyrolysis requires a considerable amount of sample (ki-lograms) and laboratory time (several weeks). In an effort to circumvent these requirements, hydrous-pyrolysis (HP) kinetic parameters for oil generation from Upper Cambrian and Tremadocian source rocks of the Baltic region are estimated by two methods: (1) organic sulfur content in kerogen and (2) HP experiments conducted at 330 and 355°C for 72 h. Estimates for the Upper Cambrian source rocks based on organic sulfur contents gave activation energies from 47 to 56 kcal/mole and frequency factors from 1.156 × 1025 to 1.078 × 1028 m.y. -1. Tremadocian source rocks based on organic sulfur content gave estimated activation energies from 60 to 62 kcal/mole and frequency factors from 1.790 × 1029 to 1.104 × 1030 m.y.-1. The estimates for the Tremadocian source rocks were less affected by thermal maturation because their low kerogen S/(S + C) mole fractions (<0.018) remained essentially constant. Conversely, the higher kerogen S/(S + C) mole fractions (>0.018) of the Upper Cambrian source rocks decreased with thermal maturation and resulted in overestimation of the kinetic parameters. The second method was designed to estimate kinetic parameters based on two HP experiments. The assump-tion that the maximum yield in calculating the rate constant at 330°C (k330°C) could be determined by a second hydrous pyrolysis experi-ment at 355°C for 72 h proved not to be valid. Instead, a previously established relationship between Rock-Eval hydrogen index and maximum HP yield for Type-II kerogen was used to calculate k330°C from oil yields generated by the HP experiment at 330°C for 72 h as-suming a first-order reaction. HP kinetic parameters were determined from relationships between k330°C and the HP kinetic parameters previously reported. These estimated HP kinetic parameters were in agreement with those obtained by the first method for immature sam-ples, but underestimated the kinetic parameters for samples at higher thermal maturities. Applying these estimated HP kinetic parameters to geological heating rates of 1 and 10°C/m.y. indicated that the Upper Cambrian source rocks would generate oil notably earlier than the overlying Tremadocian source rocks. This was confirmed in part by available data from two neighboring boreholes in the Polish sector of the Baltic. Source

Muhs D.R.,Federal Center | Budahn J.,Federal Center | Skipp G.,Federal Center | Prospero J.M.,University of Miami | And 2 more authors.
Terra Nova | Year: 2010

Africa is the most important source of dust in the world today, and dust storms are frequent on the nearby Canary Islands. Previous workers have inferred that the Sahara is the most important source of dust to Canary Islands soils, with little contribution from the Sahel region. Soils overlying a late Quaternary basalt flow on Lanzarote, Canary Islands, contain, in addition to volcanic minerals, quartz and mica, exotic to the island's bedrock. Kaolinite in the soils also likely has an exotic origin. Trace-element geochemistry shows that the soils are derived from varying proportions of locally derived basalt and African dust. Major-element geochemistry, clay mineralogy and interpretation of satellite imagery suggest that dust additions to the Canary Islands come not only from the Sahara Desert, but also from the Sahel region. © Published 2010. This article is a US Government work and is in the public domain in the USA. Source

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