Vertical Delineation of Contamination in Fractured Bedrock Aquifer

The New Jersey Department of Environmental Protection's Technical Regulations require the horizontal and vertical delineation of contamination. Monitor wells screened at increasingly deeper intervals are used to delineate vertical contamination. In New Jersey, the open interval in a bedrock well cannot exceed 7.6 m. Since contamination has been found at depths as great as 91.4 m in a production well in the study area, it would be prohibitively expensive to install monitor wells with 7.6 m open holes at ever-increasing depths until no contamination was found. Isolation of discrete zones in boreholes using pneumatic packers was implemented at a site in north central New Jersey. Ground water samples were collected from selected 6.1 m sections of boreholes drilled into fractured bedrock at three locations on the property and one offsite location. The ground water samples were analyzed in a field laboratory. The analytical results were used to determine the vertical extent of gasoline-related compounds dissolved in the ground water on the property and offsite. These compounds include benzene, ethylbenzene, methyl tertiary butyl ether, toluene, and xylenes. The four boreholes were converted into bedrock monitor wells. The intake interval for each of the wells was selected through evaluation of the vertical distribution of contaminants as determined from analytical results obtained from a field laboratory located onsite. Three wells are used for the recovery of contaminated ground water. The recovered water will be treated at the onsite air-stripping unit. The fourth well is used to chemically and hydraulically monitor the progress of the ground water recovery program.     

Web-cam’s potential for collaborative activities in the Earth sciences

We report here our experiences from using easily acquired web-cam components for collaborative ventures in the Earth sciences. We have used a variety of hardware and different software. We demonstrate from various locations in the U.S.A. the feasibility of using web-cam in multitudinous activities, relevant for conducting research and knowledge dissemination. We summarize the quality of the connections from the various combinations of communicating parties. Today, web-cams can be utilized as an economical and viable means of point-to-point communication in the Earth science community. Greater bandwidth is sorely needed for activities such as multi-party conferencing on the present internet network. We propose that web-cam can be readily deployed as a web-service for facilitating collaborative research over the GRID infrastructure, using the middleware Narada-Brokering. Web-cam will play an important role in the emerging field of geoinformatics.     

Importance of mantle derived fluids during granite associated hydrothermal circulation: He and Ar isotopes of ore minerals from Panasqueira

Helium trapped in arsenopyrite and wolframite from the Panasqueira hydrothermal deposit in central Portugal is overwhelmingly—≈ 75%—derived from the mantle. This is surprising as the W-Cu(Ag)-Sn vein deposits are spatially and temporally associated with an S-type granite. It is difficult to reconcile ³He/⁴He ratios > 5Ra (where Ra is the atmospheric ³He/⁴He ratio) with a granite produced by crustal anatexis, therefore it seems likely that mantle derived fluids unrelated to the granite were the source of the magmatic component in the ore fluids.The mantle appears to transport ³He and heat to the surface in relatively constant proportions (³He/Q = 0.1-1 x10⁻¹² cm³ STP J⁻¹). However, the ³He/heat ratios in the Panasqueira fluids (1-10 x10⁻¹² cm³ STP J⁻¹, calculated using the ³He/³⁶Ar ratio) are considerably higher. Therefore, it does not seem likely that gradual cooling of the pluton supplied heat to the hydrothermal system (as this would result in low ³He/Q ratios). Therefore, both He and heat in this collision related, granite-associated hydrothermal deposit were supplied from the mantle.     

An experimental and theoretical determination of oxygen isotope fractionation in the system magnetite-H2O from 300 to 800°C

Oxygen isotope fractionations have been determined between magnetite and water from 300 to 800°C and pressures between 10 and 215MPa. We selected three reaction pathways to investigate fractionation: (a) reaction of fine-grained magnetite with dilute aqueous NaCl solutions; (b) reduction of fine-grained hematite through reaction with dilute acetic acid; and (c) oxidation of fine iron power in either pure water or dilute NaCl solutions. Effective use of acetic acid was limited to temperatures up to about 400°C, whereas oxide-solution isotope exchange experiments were conducted at all temperatures. Equilibrium ¹⁸O/¹⁶O fractionation factors were calculated from the oxide-water experiments by means of the partial isotope exchange method, where generally four isotopically different waters were used at any given temperature. Each run product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and on a limited basis, high-resolution transmission electron microscopy (HRTEM) and Mössbauer spectroscopy. Results from the microscopic examinations indicate the formation of well-crystallized octahedra and dodecahedra of magnetite where the extent of crystallization, grain size, and grain habit depend on the initial starting material, P, T, solution composition, and duration of the run.The greatest amount of oxygen isotope exchange (∼90% or greater) was observed in experiments where magnetite either recrystallized in the presence of 0.5 m NaCl from 500 to 800°C or formed from hematite reacted with 0.5 m acetic acid at 300, 350 and 400°C. Fractionation factors (10³ ln α_mt-H2O) determined from these partial exchange experiments exhibit a steep decrease (to more negative values) with decreasing temperature down to about 500°C, followed by shallower slope. A least-squares regression model of these partial exchange data, which accounts for analytical errors and errors generated by mass balance calculations, gives the following expression for fractionation that exhibits no minimum: 1000lnα_lmt-lw=−8.984(±0.3803)x+3.302(±0.377)x²—0.426(±0.092)x³ with an R² = 0.99 for 300 ≤ T≤ 800°C (x = 10⁶/T²). The Fe oxidation results also exhibit this type of temperature dependence but shifted to slightly more negative 10³ ln α values; there is the suggestion that a kinetic isotope effect may contribute to these fractionations. A theoretical assessment of oxygen isotope fractionation using β-factors derived from heat capacity and Mössbauer temperature (second-order Doppler) shift measurements combined with known β-factors for pure water yield fractionations that are somewhat more negative compared to those determined experimentally. This deviation may be due to the combined solute effects of dissolved magnetite plus NaCl (aq), as well as an underestimation of β_mt at low temperatures. The new magnetite-water experimental fractionations agree reasonably well with results reported from other experimental studies for temperatures ≥ 500°C, but differ significantly with estimates based on quasi-theoretical and empirical approaches. Calcite-magnetite and quartz-magnetite fractionation factors estimated from the combination of magnetite β’s calculated in this study with those for calcite and quartz reported by Clayton and Kieffer (1991) agree very closely with experimentally determined mineral-pair fractionations.     

Macroscale NTIMS and microscale LA-MC-ICP-MS Re-Os isotopic analysis of molybdenite: Testing spatial restrictions for reliable Re-Os age determinations, and implications for the decoupling of Re and Os within molybdenite

We present a detailed study of Re-Os age determinations for eight natural molybdenite samples of like polytype (2H), spanning a range of age, natural grain size and deposit type. The focus of the study is to critically evaluate the effects of sampling, sample preparation and aliquant size on the accuracy and reproducibility of Re-Os ages for these molybdenite samples. We find that for some molybdenite samples, analysis of small sample aliquants (<20 mg) may not yield accurate or reproducible Re-Os ages, whereas analysis of larger aliquants from the same mineral separate do yield reproducible Re-Os dates. Such an observation is best explained if Re and ¹⁸⁷Os are internally decoupled within molybdenite grains. This finding is supported from spot analyses by laser ablation MC-ICP-MS analyses presented here and is consistent with previously published observations.The degree of decoupling between Re and ¹⁸⁷Os appears to increase both as a function of increasing grain size, and increasing age of molybdenite. From detailed dating of individual molybdenite mineral separates, we provide approximate minimum aliquant amounts required for reproducible Re-Os age dating, as a function of molybdenite age and grain size. Geologically younger, naturally fine-grained molybdenite samples appear to show little Re and ¹⁸⁷Os decoupling, and reproducible ages can be determined from some samples with as little as 1 mg of aliquant. Geologically old, and coarse-grained molybdenite samples may require as much as 40 mg of aliquant from a much larger mineral separate to overcome Re and ¹⁸⁷Os decoupling. The mechanism(s) of Re and ¹⁸⁷Os decoupling within molybdenite is not constrained by this results of this study, but the observation that the degree of decoupling increases with grain size (distance) and age (time/geologic history) may suggest primary diffusive control. Assuming that Re and ¹⁸⁷Os decoupling in molybdenite results primarily from diffusion of ¹⁸⁷Os, apparent diffusion coefficients are calculated (D = x²/t). Estimates of D for Os made in this way range from 2.8 × 10⁻²⁶ to 2.1 × 10⁻²¹ m²/s, which are broadly similar to experimentally derived diffusion coefficients for Os in Fe-sulfide minerals and for Re in molybdenite at temperatures <500°C.     

Revision of the conchostracan genera Cratostracus and Porostracus from Cretaceous deposits in north-east China

The diagnoses of the conchostracan genera Cratostracus and Porostracus are revised following a re-examination of their type species under a scanning electron microscope. In Cratostracus each growth line has a serrated lower margin. Radial lirae branch into smaller ridges that merge with each other to give the upper part of each growth band in the ventral region of the carapace a slightly undulating surface. Cross-bars are present between these lirae. In Porostracus the radial lirae on the growth bands near the umbo are long and relatively widely spaced. There is a fine reticulum between them in the umbonal part of the carapace and cross-bars on the ventral surface. The ornament of Porostracus indicates that it can be assigned to the family Halysestheriidae rather than to the Afrograptidae, in which it has been placed previously. Morphological analysis of most of the species of the two genera and closely related Orthestheria (Migransia) under the scanning electron microscope is required before their stratigraphic potential can be fully realized.     

Émergence de la complexité dans un modèle simple de comportement mécanique des roches

We propose a mechanical model for the behaviour of rocks based on progressive damage at the elementary scale and elastic interaction. It allows us to simulate several experimental observations: mechanical behaviour ranging from brittle to ductile, fractal structure of the damage, power-law distribution of the damage avalanches. These macroscopic properties are not incorporated at the elementary scale, but are the results of the interaction between elements. This emerging complexity permits us to consider the strain rock process as a complex system characterized by non-linear dynamics. To cite this article: D. Amitrano, C. R. Geoscience 336 (2004).     

Pliocene and Quaternary regional uplift in western Turkey: the Gediz River terrace staircase and the volcanism at Kula

Along the upper reaches of the Gediz River in western Turkey, in the eastern part of the Aegean extensional province, the land surface has uplifted by 400 m since the Middle Pliocene. This uplift is revealed by progressive gorge incision, and its rate can be established because river terraces are capped by basalt flows that have been K–Ar and Ar–Ar dated. At present, the local uplift rate is 0.2 mm a⁻¹. Uplift at this rate began around the start of the Middle Pleistocene, following a span of time when the uplift was much slower. This was itself preceded by an earlier uplift phase, apparently in the late Late Pliocene and early Early Pleistocene, when the uplift rate was comparable to the present. The resulting regional uplift history resembles what is observed in other regions and is analogously interpreted as the isostatic response to changing rates of surface processes linked to global environmental change. We suggest that this present phase of surface uplift, amounting so far to 150 m, is being caused by the nonsteady-state thermal and isostatic response of the crust to erosion, following an increase in erosion rates in the late Early Pleistocene, most likely as a result of the first large northern-hemisphere glaciation during oxygen isotope stage 22 at 870 ka. We suggest that the earlier uplift phase, responsible for the initial 250 m of uplift, resulted from a similar increase in erosion rates caused by the deterioration in local climate at 3.1 Ma. This uplift thus has no direct relationship to the crustal extension occurring in western Turkey, the rate and sense of which are thought not to have changed significantly on this time scale. Our results thus suggest that the present, often deeply incised, landscape of western Turkey has largely developed from the Middle Pleistocene onwards, for reasons not directly related to the active normal faulting that is also occurring. The local isostatic consequences of this active faulting are instead superimposed onto this “background” of regional surface uplift. Modelling of this surface uplift indicates that the effective viscosity of the lower continental crust beneath this part of Turkey is of the order of 10¹⁹ Pa s, similar to a recent estimate for beneath central Greece. The lower uplift rates observed in western Turkey, compared with central Greece, result from the longer typical distances of fluvial sediment transport, which cause weaker coupling by lower-crustal flow between offshore depocentres and eroding onshore regions that provide the sediment source.     

Statewide Estimates of Undiscovered Deposits of Gold,Silver, Copper,Lead, and Zinc

Estimates of the number of undiscovered deposits on a statewide basis offer a different perspective on the nation's undiscovered resources of gold, silver, copper, lead, and zinc. Mean estimates of the number of undiscovered deposits statewide were extracted from the estimates of undiscovered deposits nationwide. More than 50 undiscovered deposits are estimated to occur in Alaska, Arizona, Nevada, and Wisconsin. Estimating the number of undiscovered deposits statewide serves as a measure of a state's total remaining mineral resources in known conventional deposit types.