St. Louis Meeting     

Robert A. Harper 《The Professional geographer》1967,19(1):23-23

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Sulfur isotopic zonation in the Cadia district,southeastern Australia: exploration significance and implications for the genesis of alkalic porphyry gold–copper deposits     

Alan J. Wilson  David R. Cooke  Benjamin J. Harper  Cari L. Deyell 《Mineralium Deposita》2007,42(5):465-487

The alkalic porphyry gold–copper deposits of the Cadia district occur in the eastern Lachlan Fold Belt of New South Wales, Australia. The district comprises four porphyry deposits (Ridgeway, Cadia Quarry, Cadia Hill, and Cadia East) and two iron–copper–gold skarn deposits (Big Cadia and Little Cadia). Almost 1,000 tonnes of contained gold and more than four million tonnes of copper have been discovered in these systems, making Cadia the world’s largest known alkalic porphyry district, in terms of contained gold. Porphyry gold–copper ore at Cadia is associated with quartz monzonite intrusive complexes, and is hosted by central stockwork and sheeted quartz–sulfide–(carbonate) vein systems. The Cadia porphyry deposits are characterized by cores of potassic and/or calc–potassic alteration assemblages, and peripheral halos of propylitic alteration, with late-stage phyllic alteration mostly restricted to fault zones. Hematite dusting is an important component of the propylitic alteration assemblage, and has produced a distinctive reddening of feldspar minerals in the volcanic wall rocks around the mineralized centers. Sulfide mineralization is strongly zoned at Ridgeway and Cadia East, with bornite-rich cores surrounded by chalcopyrite-rich halos and peripheral zones of pyrite mineralization. The Cadia Hill and Cadia Quarry deposits have chalcopyrite-rich cores and pyrite-rich halos, and Cadia Hill contains a high-level bornite-rich zone. Distinctive sulfur isotopic zonation patterns have been identified at Ridgeway, Cadia Hill, and Cadia East. The deposit cores are characterized by low δ³⁴S_sulfide values (−10 to −4‰), consistent with sulfide precipitation from an oxidized (sulfate-predominant) magmatic fluid at 450 to 400°C. Pyrite grains that occur in the propylitic alteration halos typically have δ³⁴S_sulfide values near 0‰. There is a gradual increase in δ³⁴S_sulfide values outwards from the deposit cores through the propylitic halos. Water–rock interaction during propylitic alteration caused magmatic sulfate reduction and concomitant oxidation of ferrous iron-bearing minerals, resulting in enrichment of ³⁴S in pyrite and also producing the distinctive reddened, hematite-rich alteration halos to the Cadia deposits. These results show that sulfur isotope analyses have potential applications in the exploration of alkalic porphyry-style deposits, with zones of depleted δ³⁴S_sulfide values most prospective for high-grade mineralization.  相似文献   

Superposed deposits of thick coal on the eastern edge of the Illinois Basin and their association with underlying geologic features     

D Harper  G.A Olyphant 《International Journal of Coal Geology》1991,17(3-4)

Comparison of maps produced from publicly available data (drillers' logs, electrical logs and mine maps) provides a basis for inferring a deep-seated influence on the distribution of superposed deposits of thick coal (>1.4 m) in four Middle Pennsylvania (Desmoinesian Series) coal beds in three mining districts of west-central Indiana. Thick sandstone (>18 m) is common in areas between and around the mining districts, but less than 3 percent of the study area (consisting of 3200 km²) is underlain by both thick coal and thick sandstone. Only thick sandstone associated with the Survant Coal Member (Linton Formation), and informally referred to by us “Survant sandstone”, exists in all of the thin-coal areas. After comparison with published maps by other authors, it is inferred that distribution of the Survant sandstone, which was deposited immediately after a long period of slow deposition associated with the Colchester Coal Member (Linton Formation), may reflect topographic expression of long-term subsidence associated with differential thinning of much deeper Silurian strata (580 m below).Although the findings of this study provide the basis for a conceptual geologic model with a hypothetical structure that is amenable to statistical testing, such analysis should be undertaken only after the data are analyzed for randomness, spatial autocorrelation, linearity and normality.  相似文献   

Estimation of Pore Water Concentrations from DGT Profiles: A Modelling Approach   总被引：2，自引：0，他引：2  

Michael P. Harper  William Davison  Wlodek Tych 《Aquatic Geochemistry》1999,5(4):337-355

The technique of Diffusional Gradients in Thin-films (DGT) can be used in situ to obtain high resolution profiles of trace-metals in sediment pore waters. Substances sampled by DGT continuously diffuse through a diffusion layer comprising a hydrogel prior to being immobilized by binding to a resin layer. DGT therefore measures a time averaged flux from the pore water to the resin. Interpretation of this flux as pore water concentration is problematic for two reasons. Firstly, the pore water concentration adjacent to the sampler may become depleted by the DGT induced flux. Secondly, if there are steep vertical chemical gradients in the pore waters, they may relax by diffusion along the gradient within the gel layer. The extent of relaxation depends on the diffusion coefficient, gradient steepness, and diffusion layer thickness. Two dimensional (2D) numerical models of DGT deployments in horizontally uniform sediments were used to investigate to what extent DGT measured profiles accurately reproduced (a) the shape of pore water concentration profiles, and (b) the magnitude of pore water concentrations. A method is developed which translates high resolution DGT measured flux profiles into reliable estimates of pore water concentrations. Linear relationships are given which estimate the minimum DGT measured peak width (as a function of diffusion layer thickness) that ensures accurate reproduction of the shape and the magnitude of peaks in pore water concentrations. Peaks in DGT profiles obtained from assemblies with diffusion layer thicknesses of 0.3 mm (0.5 mm) should be at least 1.2 mm (1.8 mm) wide for their shape to reflect accurately their true shape in the pore water, and at least 1.7 mm (2.7 mm) wide to ensure the peak concentration is accurately estimated.  相似文献   

Hydrologic changes associated with the October 28, 1983, Idaho earthquake     

R. L. Whitehead  R. W. Harper  H. G. Sisco 《Pure and Applied Geophysics》1984,122(2-4):280-293

Significant hydrologic changes were observed after the magnitude 7.3 earthquake that occurred on October 28, 1983, in central Idaho. Groundwater levels rose by as much as 3 meters near the epicenter. Discharge in many streams and springs increased, in some instances by more than 100%. One warm spring ceased flowing for several days; the flow then resumed and peaked at about nine times its original rate. Available data show no significant changes in water quality following the earthquake.  相似文献   

Characterization of coal maceral concentrates by curie-point pyrolysis mass spectrometry     

Henk L.C. Meuzelaar  Alice M. Harper  Ronald J. Pugmire  Jirina Karas 《International Journal of Coal Geology》1984,4(2):143-171

A set of 30 maceral concentrates consisting of 5 exinites (sporinites), 14 vitrinites and 11 inertinites (fusinites and semifusinites) was analyzed by Curie-point pyrolysis mass spectrometry in combination with computerized multivariate statistical analysis techniques. Seventeen samples, representing sink/flotation concentrates of 7 different coals, were obtained through the British National Coal Board, whereas the remaining samples represent cesium-chloride density-gradient centrifugation fractions of two different U.S. coals prepared at the University of Utah.It is found that vitrinites, (semi)fusinites and, to some extent, sporinites show qualitatively similar rank-related changes, such as a decrease in dihydroxybenzene signals and an increase in napthalene signals with increasing rank. In fact, the overall pyrolysis MS patterns of inertinities show a close similarity to those of vitrinites of corresponding carbon content (as obtained from higher rank coals).Notwithstanding these similarities, however, the presence of basic differences in maceral structure is indicated by relatively minor but characteristic peak series in the liptinite (sporinite) as well as inertinite samples. Whereas inertinite spectra show relatively pronounced peak series at the high mass end of the spectrum which can be tentatively identified as representative of polynuclear aromatic compounds, sporinites are characterized by series of branched aliphatic and/or alicyclic polyenic hydrocarbons, possibly representing isoprenoids and related biomarker compounds.  相似文献   

Vulnerability and adaptive capacity of Inuit women to climate change: a case study from Iqaluit,Nunavut     

Anna Bunce  James Ford  Sherilee Harper  Victoria Edge  IHACC Research Team 《Natural Hazards》2016,83(3):1419-1441

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Assessment of a shell bank and associated substrates as nursery habitat of postsettlement red snapper     

J. R. Rooker  A. M. Landry  Jr.  B. W. Geary  J. A. Harper 《Estuarine, Coastal and Shelf Science》2004,59(4):653-661

Trawl surveys were conducted in 2000 and 2001 to examine patterns of distribution and abundance of postsettlement red snapper (Lutjanus campechanus) on a shell bank, Freeport Rocks Bathymetric High (FRBH), in the northwestern Gulf of Mexico. In addition, otolith-based methods were used to determine age, hatch-date, growth and mortality of new recruits associated with FRBH. Date and region were significant factors affecting density of red snapper in 2000. Peak densities of red snapper were observed in July and August, and mean density among habitat types (shell bank, inshore mud, offshore mud) was similar (range: 50–52 ind hectare⁻¹) in 2000. Alternatively, a habitat effect was detected during a limited survey conducted in 2001, with density higher on the shell bank than inshore or offshore mud habitat. Postsettlement red snapper were first detected at approximately 16 mm standard length, and individuals less than 20 mm were present in all habitats. Estimated ages of red snapper ranged from 26 to 121 d, with new settlers (≤20 mm) typically less than 28 d. Predicted hatch dates ranged from early April to mid August with a single peak occurring from late May to early June. Growth rate for the April–May cohort (0.817 mm d⁻¹) was similar to the June–July cohort (0.830 mm d⁻¹). Habitat-specific differences in growth were observed, and rates were highest for individuals from the inshore habitat (0.881 mm d⁻¹). Mortality rates (Z) during the early post-settlement period were approximated using catch curves, and early life mortality of red snapper was 12.1% d⁻¹ (Z=0.129). While the difference in mortality between cohorts was negligible, a habitat-specific difference in mortality was observed. Mortality rate of red snapper inhabiting the inshore mud habitat (Z=0.045, 4.4% d⁻¹) was lower than rates observed for individuals on the shell bank (Z=0.120, 11.9% d⁻¹) or offshore (Z=0.099, 9.3% d⁻¹) habitat. Individuals residing in the inshore habitat had significantly higher growth rates and significantly lower mortality rates, suggesting that recruitment potential was higher for these individuals.  相似文献   

The accuracy of surface elevations in forward global barotropic and baroclinic tide models     

Brian K. Arbic  Stephen T. Garner  Robert W. Hallberg  Harper L. Simmons   《Deep Sea Research Part II: Topical Studies in Oceanography》2004,51(25-26):3069

This paper examines the accuracy of surface elevations in a forward global numerical model of 10 tidal constituents. Both one-layer and two-layer simulations are performed. As far as the authors are aware, the two-layer simulations and the simulations in a companion paper (Deep-Sea Research II, 51 (2004) 3043) represent the first published global numerical solutions for baroclinic tides. Self-consistent forward solutions for the global tide are achieved with a convergent iteration procedure for the self-attraction and loading term. Energies are too large, and elevation accuracies are poor, unless substantial abyssal drag is present. Reasonably accurate tidal elevations can be obtained with a spatially uniform bulk drag c_d or horizontal viscosity K_H, but only if these are inordinately large. More plausible schemes concentrate drag over rough topography. The topographic drag scheme used here is based on an exact analytical solution for arbitrary small-amplitude terrain, and supplemented by dimensional analysis to account for drag due to flow-splitting and low-level turbulence as well as that due to breaking of radiating waves. The scheme is augmented by a multiplicative factor tuned to minimize elevation discrepancies with respect to the TOPEX/POSEIDON (T/P)-constrained GOT99.2 model. The multiplicative factor may account for undersampled small spatial scales in bathymetric datasets. An optimally tuned multi-constituent one-layer simulation has an RMS elevation discrepancy of 9.54 cm with respect to GOT99.2, in waters deeper than 1000 m and over latitudes covered by T/P (66N to 66S). The surface elevation discrepancy decreases to 8.90 cm (92 percent of the height variance captured) in the optimally tuned two-layer solution. The improvement in accuracy is not due to the direct surface elevation signature of internal tides, which is of small amplitude, but to a shift in the barotropic tide induced by baroclinicity. Elevations are also more accurate in the two-layer model when pelagic tide gauges are used as the benchmark, and when the T/P-constrained TPXO6.2 model is used as a benchmark in deep waters south of 66S. For Antarctic diurnal tides, the improvement in forward model elevation accuracy with baroclinicity is substantial. The optimal multiplicative factor in the two-layer case is nearly the same as in the one-layer case, against initial expectations that the explicit resolution of low-mode conversion would allow less parameterized drag. In the optimally tuned two-layer M₂ solution, local values of the ratio of temporally averaged squared upper layer speed to squared lower layer speed often exceed 10.  相似文献   

奥陶系上统赫南特阶全球层型剖面和点位的建立   总被引：6，自引：0，他引：6  

陈旭  戎嘉余  樊隽轩  詹仁斌  C. E. Mitchell  D. A. T. Harper  M. J. Melchin  彭平安  S. C. Finney  汪啸风 《地层学杂志》2006,30(4):T0001-T0002

赫南特阶(上奥陶统)的全球界线层型剖面和点位确立在中国宜昌王家湾北剖面观音桥层底界之下0.39m处。该剖面位于中国湖北省宜昌市以北42km处的王家湾村,经纬度为30°58′56″N、111°25′10″E。赫南特阶底界的GSSP点位以笔石Normalograptusextraordinarius的首次出现层位(FAD)为标志。碳同位素在此层位显示的正漂移以及N.ojsuensis的首现可作为第二标志。赫南特阶始于自Diceratograptusmirus亚带开始的全球生物大灭绝事件的主幕之后。王家湾北剖面出露完整,沉积和生物序列连续,笔石和壳相动物化石丰富并保存良好,王家湾北、王家湾南和王家湾小河边剖面都发育了合适的沉积相和生物相并具有广泛对比的潜力。该地区地质构造简单,岩石未经历较强的变质作用,且交通便利。王家湾小河边剖面尤其适合进行化学地层学研究和同位素年龄的测定。建立赫南特阶底界的全球界线层型剖面和点位的提案报告于2004年10月被国际地层委员会奥陶系分会通过,经补充完善后,于2006年2月被国际地层委员会通过,同年5月被国际地科联正式批准。  相似文献