Raymond M. Coveney

Rhenium and osmium isotopes in black shales and Ni-Mo-PGE-rich sulfide layers, Yukon Territory, Canada, and Hunan and Guizhou provinces, China

Rhenium and osmium abundances and osmium isotopic compositions were determined by negative thermal ionization mass spectrometry for samples of Devonian black shale and an associated Ni-enriched sulfide layer from the Yukon Territory, Canada. The same composition information was also obtained for samples of early Cambrian Ni-Mo-rich sulfide layers hosted in black shale in Guizhou and Hunan provinces, China. This study was undertaken to constrain the origin of the PGE enrichment in the sulfide layers. Samples of the Ni sulfide layer from the Yukon Territory are highly enriched in Re, Os, and other PGE, with distinctly higher Re/192Os but similar Pt/Re, compared to the black shale host. Re-Os isotopic data of the black shale and the sulfide layer are approximately isochronous, and the data plot close to reference isochrons which bracket the depositional age of the enclosing shales. Samples of the Chinese sulfide layers are also highly enriched in Re, Os, and the other PGE. Re/192Os are lower than in the Yukon sulfide layer. Re-Os isotopic data for the sulfide layers lie near a reference isochron with an age of 560 Ma, similar to the depositional age of the black shale host. The osmium isotopic data suggest that Re and PGE enrichment of the brecciated sulfide layers in both the Yukon Territory and in southern China may have occurred near the time of sediment deposition or during early diagenesis, during the middle to late Devonian and early Cambrian, respectively.

Serpentinization and the Origin of Hydrogen Gas in Kansas

Hydrogen gas occurs in ten Kansas wells near the Mid-Continent rift system. Since 1982, two wells have yielded small amounts of gases containing an average of 29-37 mole % H2, the remainder being chiefly N2 with only traces of hydrocarbons. Isotopic compositions for hydrogen (^dgrD = -740 to -836 ^pmil) imply near-ambient (about 10°C) equilibration temperatures for the gases, which are among the most deuterium-depleted in nature and resemble the H2-rich gases described from ophiolites in Oman. Isotopic values for the Kansas N2 differ slightly from those of the atmosphere, but not enough to rule out an atmospheric origin. Because they are low in CH4 and CO2, expected byproducts of biogenic activity, the gases are probably abiogenic in origin. The existence of such gases near a major rift system, containing mafic rocks, and not far from known kimberlites is consistent with an origin from reactions involving Fe+2 oxidation, for example during serpentinization. Because the gases may be associated with kimberlites and deep-seated rifting, mantle outgassing is possible, but such an origin would be difficult to reconcile with the low isotopic temperatures. The H2 gases from Kansas (and elsewhere) seem to be too low in pressure to have commercial value. However, neither the Kansas gases nor those from other H2 occurrences have been adequately examined to assess their importance as potential resources.

Environmental quality assessment on a river system polluted by mining activities

In this study, adverse impacts of heavy metal pollution, originating from mining, smelting and panning activities, on the aquatic ecosystem of the Lean River in south China, were evaluated by integrating the chemical, toxicological and ecological responses of single and multiple metals in overlying water, surface sediment and floodplain topsoil. The assessment results indicated that a highly localized distribution pattern was closely associated with the pollution sources along the river bank. Based on the combined indices, deterioration of local environmental quality was induced mainly by two sources. One was strong acidity and a large amount of Cu in the drainage from the Dexing Cu Mine. Another was high concentrations of Pb and Zn in the effluents released from many smelters and mining/panning activities in the riparian zone. Some possible suggestions on source control may be effective in dealing with these issues.

A review of the origins of metal-rich Pennsylvanian black shales, central U.S.A., with an inferred role for basinal brines

Abstract Compared to most shales, even most black shales, numerous thin Pennsylvanian marine black shales of the U.S. Midwest are very enriched in organic C (5–40wt%) and heavy elements. For example, instrumental neutron activation analysis of 74 samples of mostly black and dark gray Pennsylvanian shales of the U.S. Midwest average 1300 ppm Zn, 85 ppm U, 655 ppm Mo, 130 ppm Se and 55 ppm Cd—amounts sufficient to raise concerns about heavy element pollution. Direct precipitation of sulfides and fixation by abundant organic matter during sedimentation and early diagenesis may account for heavy metals contained by shales in most cases. Metal supply calculations, however, indicate that a special source would be needed to supply metals for a strictly syngenetic origin. Possible sources for such metals include submarine hot springs and Pennsylvanian seas that may have been more enriched in metals than modern ocean water. At least at some localities, additional metal values may have been added later from basinal brines (e.g. Zn) or from modern groundwaters (e.g. Mo, Se, U). The actions of modern supergene processes may fix metals, mitigating detrimental effects from black shales.

Complex refractive index of limestone in the visible and infrared

Near normal-incidence relative spectular reflectance was measured throughout the 0.2-32.8-microm wavelength region for three cut and polished samples of Bethany Falls limestone. Water, for which the complex refractive index is well known, was the reflectance standard. Although the visual appearances of the three samples were quite different, the relative reflectance spectra for the three samples were nearly identical. The three relative reflectance spectra were averaged to obtain a composite relative reflectance spectrum. Kramers-Kronig analysis of the composite relative reflectance spectrum then provided spectral values of the complex refractive index for limestone. A classical Lorentz dispersion analysis was also made of the composite relative reflectance spectrum, and the resulting dispersion parameters were tabulated. Infrared bands characteristic of the carbonate ion CO(3)(-2) of the calcite comprising the limestone appeared as strong features in the spectra.

Cyclic variations of sulfur isotopes in Cambrian stratabound Ni-Mo- ( PGE-Au) ores of southern China

Abstract Cyclic variations of δ 34 S values over a range of at least 48‰ in pyrite nodules from stratabound Ni-Mo-PGE(Au) ores of southern China are attributed to biogenic reduction of seawater sulfate in an anoxic, phosphogenic, and metallogenic basin. Cyclic introduction and mixing of normal seawater into typically stagnant basin waters led to extreme variations in δ 34 S values of aqueous sulfide species present at different times. Intermittent venting of metal-laden hydrothermal fluids into such a bacteriogenic sulfide-rich environment resulted in precipitation of metal sulfides as pseudomorphous replacements of organic debris and as sulfide sediments that record large δ 34 S CDT variations from −26 to +22‰. Apatite and silica dominated the replacement of the organic debris when metals were not being introduced into the basin. The combination of abundant organic debris, localized topographic basins for accumulation of the debris, bacterial production of sulfide species, and introduction of metal-bearing hydrothermal fluids provided the environment necessary to form these unusually rich Ni-Mo ores.

Contrasting depositional models for Pennsylvanian black shale discerned from molybdenum abundances

Some black shales contain >1,000 ppm Mo, comparable to conventional ores. These include Mo-rich Pennsylvanian black shales that were deposited rapidly near shore as epeiric seas inundated peat swamps, while coeval beds, less enriched in Mo, accumulated slowly offshore. Concentration of Mo probably resulted from retention of the metal by organic matter in acidic pore fluids characteristic of nearshore deposits. Thus, in Pennsylvanian shales where organic productivity is significant, Mo variations may be used to distinguish nearshore from offshore conditions. Enrichments in Mo occur in black shales of other ages; therefore a high Mo content may be useful as a general criterion for nearshore environments and other conditions with strong pH gradients.

A C/MoS2 mixed-layer phase (MoSC) occurring in metalliferous black shales from southern China, and new data on jordisite

Abstract A new phase composed mainly of Mo, S, and C and referred to herein as MoSC occurs widely in organic-rich, metalliferous Cambrian black shales in south China. MoSC, which has previously been referred to as jordisite, has been studied by scanning electron microscopy (SEM), electron microprobe analysis (EMPA), transmission electron microscopy (TEM), powder X-ray diffraction, (XRD), extended X-ray absorption fine structure (EXAFS), and catalytic activity. TEM data show MoSC to have a layered structure, with packets resembling molybdenite and graphite-like carbon that average five layers in thickness. Analytical data are consistent with an idealized formula of Mo3S6C10 but it commonly contains 1-3 wt% each of Fe, Ni, and As so that its composition may be better approximated by the formula (Mo,Fe,Ni)3(S,As)6C10. Selected area electron diffraction (SAED) patterns show a small number of broad, inhomogeneous rings corresponding to randomly oriented layers arranged in subspherical cells. A single broad, weak peak corresponds to a 10-11 Å layer spacing in powder XRD diffraction patterns. Pseudomorphism after fossil bacteria implies an origin by replacement of sedimentary organic material. In its chemical properties and structure, MoSC resembles synthetic compounds used as catalysts for hydrodesulfurization (HDS) in the petrochemical industry. The large surface-to-volume ratio for MoSC may be an important factor in its relatively strong HDS catalytic activity. Cotype samples of jordisite from Germany, previously thought to be amorphous MoS2, were also studied by SEM and TEM. Jordisite occurs as sequences of a few curved layers that form subspherical units, with an appearance remarkably like that of MoSC. However, the layer spacing is ~6 Å, like that of molybdenite. The ratio of Mo:S is ~1:2, and no carbon was detected, although it coexists with kerogen. Jordisite is thus confirmed to be a form of MoS2, but because powder diffraction- like SAED patterns were obtained, it is not amorphous.

Organochlorine pesticide residuals in chickens and eggs at a poultry farm in Beijing, China

Chicken organs, animal feed, droppings, and ambient air were sampled at a farm in Beijing to determine the concentrations of hexachlorocyclohexane isomers (HCHs) and dichlorodiphenyltrichloroethane and metabolites (DDTs). Mean fresh weight concentrations of HCHs and DDTs were 0.122+/-0.061 ng/g and 0.051+/-0.038 ng/g in the muscles. These values are 1-2 orders of magnitude lower than those reported in China in 1980. Contaminated feed was the main source of HCHs and DDTs. Only 12.8% of HCH and 3.3% of DDT of the amount consumed were excreted. Accumulated quantities of HCHs and DDTs increased during growth. However, concentrations of HCHs and DDTs did not increase because of dilution from rapid growth. Based on the observed residual levels in mature chicken and the average diet of residents of China, the contributions from chicken and egg consumption to per capita daily intake of HCHs and DDTs were 487% and 88% of those of fish consumption.

Th-Pb and U-Pb Dating of Ore-Stage Calcite and Paleozoic Fluid Flow

Thorium-232-lead-208 and uranium-238-lead-206 radiometric ages for ore-stage calcite show that Mississippi Valley-type (MVT) ore deposits can form in distinct tectonic settings. An age of 251 ± 11 million years for the Jumbo Mine in Kansas, United States, is in agreement with other ages for MVT deposits in the midcontinent of North America. The similarity of ages of these deposits supports the concept that they formed in response to fluid flow during the late Paleozoic Alleghenian-Ouachita orogeny. An age of 351 ± 15 million years for Twelve Mile Bore and Bloodwood-Kapok deposits in Australia indicates that these MVT ores were deposited in a rifting environment.