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61.
Recent mineral exploration in the McArthur River District, Northern Territory, has found new areas of base‐metal mineralization and has resulted in a reinterpretation of the geological setting of the previously discovered mineral deposits. The geology along the eastern margin of the H.Y.C. sub‐basin has been revised. The Cooley Dolomite Member of the Barney Creek Formation is interpreted as a talus‐slope breccia lying adjacent to a syndepositionally uplifted fault block (Western Fault Block) of lower McArthur Group sediments. The Western Fault Block was the source of the majority of the fragments in breccia horizons in the H.Y.C. sub‐basin and its uplift played an important role in the development of the sub‐basin. Within the Western Fault Block, the sequence hosting the Cooley II copper mineralization is the Mara Dolomite Member of the Emmerugga Dolomite, and not the Cooley Dolomite Member of the Barney Creek Formation as previously thought. New mineral discoveries include the substantial extension of the Coxco deposit, a coarse‐grained zinc‐lead stratabound deposit showing affinities with the Mississippi Valley‐type deposits; and an area of stratiform fine‐grained zinc‐lead mineralization in the Emu Plains sub‐basin of the Bulburra Depression. 相似文献
62.
Differences in the reporting units of data from diverse sources and changes in units over time are common obstacles to analysis of areal data. We compare common approaches to this problem in the context of changes over time in the boundaries of U.S. census tracts. In every decennial census, many tracts are split, consolidated, or changed in other ways from the previous boundaries to reflect population growth or decline. We examine two interpolation methods to create a bridge between years, one that relies only on areal weighting and another that also introduces population weights. Results demonstrate that these approaches produce substantially different estimates for variables that involve population counts, but they have a high degree of convergence for variables defined as rates or averages. Finally, the article describes the Longitudinal Tract Database (LTDB), through which we are making available public-use tools to implement these methods to create estimates within 2010 tract boundaries for any tract-level data (from the census or other sources) that are available for prior years as early as 1970. 相似文献
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Sulfur isotopic compositions were determined by ion microprobe for 36 spots on anhydrite crystals in trachyandesitic pumices erupted from El Chichón Volcano in 1982. Individual anhydrite crystals are homogeneous in δ34S, within the ±1‰ (2σ) uncertainty of the method, but crystal-to-crystal variations are large (+2.5 to +10.9‰). The mean δ34S for anhydrite (+6.4 ± 2.1‰, 1σ) is significantly lower than earlier results for bulk anhydrite separates (+9.0 to +9.2‰). The difference between the mean δ34S values in these two populations may reflect a grain-size effect, with heavier sulfur concentrated in smaller anhydrite crystals, few of which were analyzed by ion microprobe. Variations in δ34S show no correlation with complex textures in anhydrite revealed by cathodoluminescence color. Ion-microprobe analyses of δ34S were also obtained on six ovoid-shaped inclusions of pyrrhotite, chalcopyrite, and/or intermediate sulfide solid solution hosted by silicate or oxide crystals, interpreted to be magmatic (δ34S = −0.1 to +2.7‰; mean +0.7‰), and on four irregularly shaped multiphase sulfide fragments in the matrix, interpreted as xenocrystic, which range widely in δ34S (−3.7 to +5.5‰). We evaluate four different mixing scenarios involving (1) magmatic anhydrite and sedimentary sulfate, (2) magmatic anhydrite and hydrothermal anhydrite, and anhydrite and coexisting sulfide crystals precipitated in different domains of a common magma reservoir that were affected by (3) different degrees of degassing or (4) different degrees of crustal sulfur contamination. The model involving physical contamination of sedimentary sulfate is considered untenable. The other three models are considered to be viable, but none of them can explain all observations. The results of this study and other recent investigations prompt a re-evaluation of the sulfur budget for the 1982 El Chichón eruption. We estimate that 2.2 × 1013 g of S was emitted, and that 58 wt.% of the sulfur was present as anhydrite prior to eruption, with the remainder in a vapor phase, with H2S/SO2 ≈ 9. The bulk magmatic δ34S value for the 1982 El Chichón trachyandesite is estimated as +4.1 to +5.8‰, typical of the relatively heavy sulfur isotopic compositions that characterize subduction-related magmas. 相似文献
67.
Groundwater of the coastal plain of the Rio de La Plata, Argentina,contains up to 17 g L-1 SO4 and 37 gL-1 TDS. Some of this SO4 is from paleo-seawater intrusion; however, SO4 : Cl ratios can be>2 : 1, and most of the SO4 must, therefore, have another source. Three possible sources were investigated: gypsum, organic matter,and iron sulphides.
Dissolved SO4 showed δ34S valuesfrom -7 to 0‰, typical values for S from iron sulphides or organicmatter, but distinct from that of seawater (+22‰).
To test whetherthe SO4 was derived from oxidation of reduced S, four 4-mcores were taken from marine sediments of the coastal plain. Two were takenfrom
higher, drier areas where the highest dissolved SO4values were encountered, and two were taken from lower, wetter areas thathad much lower SO4 concentrations. Pore waterSO4, Cl and alkalinity were determined; solids were analyzedfor SO4, sulphide-S and organic-S.
Sulphide-S was the dominant form of reduced S, averaging about0.5% S in the lower interval (2.5–4 m) of the cores. Sulphidewas
absent in the upper 2.5 m in both topographically higher and lowerareas. Sulphate was present in the entire unit in the higher,
drier areas,but almost absent in lower areas. Organic-S was insignificant.
Our model for the origin of dissolved SO4 is: fine-grainedpyrite was oxidized during hotter or drier periods. Some resulting dissolvedSO4 was precipitated as gypsum. Iron from the pyriteprecipitated as FeOOH. Lower, wetter areas formed over time where recharginggroundwater
dissolved most of the gypsum. In higher areas with low hydraulicgradients and high net evapotranspiration, SO4 remained asgypsum and in the dissolved phase.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
68.
During 1994 a project was initiated by Ordnance Survey to investigate the requirement for completing the multi-million pound digital revision of 1:2500 scale mapping within Great Britain. This paper, although concentrating on this scale of mapping, discusses the revision policy issues that faced Ordnance Survey and the practical implications arising from implementing the policy for its 1:2500 and 1:10 000 basic scale mapping. Use of contractors was seen as a prime requirement as the resources available within Ordnance Survey were not sufficient to implement the full revision programme. This paper discusses the background to the task and considers the range of photogrammetric options and contractual and quality procedures required for the revision of the mapping over the next few years. 相似文献
69.
Alan Logan 《Marine Ecology》2004,25(3):207-215
Abstract. The lacazelline brachiopod Pajaudina , with type species P. atlantica , was originally described by the author in 1988 from dead and transported shells collected by Dutch CANCAP expeditions to the Canary Islands. Living sites have now been discovered in shallow-water caves on El Hierro and La Palma in the Canary Islands. From photographs and specimens, information has been obtained on life habits and associated biota, the nature of the ptycholophe lophophore, sexually dimorphic characters of the shell and ontogenetic growth stages of the dorsal valve. The latter are shown to be similar to those of Lacazella , as exemplified by L. caribbeanensis from the Bahamas, up to the penultimate stage, following which there are repeated furcations of the minor interbrachial lobes not seen in Lacazella but present in Ospreyella Lüter & Wörheide. 相似文献
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