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101.
Christopher J. Yeats Ernst A. Kohler Neal J. McNaughton Luke J. Tkatchyk 《Mineralium Deposita》2001,36(2):125-136
The 7 million oz. Jundee–Nimary lode-gold deposit occurs in the northern portion of the Yandal greenstone belt in the northeastern
part of the Archean Yilgarn Craton of Western Australia. Gold mineralization at Jundee–Nimary is similar in structural style,
mineralogy, geochemistry and relative timing with respect to deformation and metamorphism, to other Western Australian Archean
greenstone-hosted gold deposits, but is unusual in the fact that mineralized structures are crosscut by structurally late
intermediate to felsic dykes. Within the Deakin South open cut, gold mineralization is hosted in brittle–ductile shear zones
primarily developed within the dacitic Mitchell Porphyry. The Moore Porphyry, a broad dyke of porphyritic granodiorite, intrudes
the Mitchell Porphyry, crosscutting and post-dating gold mineralization. Analytically indistinguishable SHRIMP U–Pb zircon
ages of 2678 ± 5 Ma for the Mitchell Porphyry and 2669 ± 7 Ma for the Moore Porphyry require that gold mineralization at Jundee–Nimary
occurred at ca. 2680–2660 Ma, approximately 40 million years earlier than the majority of published robust ages for gold mineralization
in the Yilgarn Craton, which mostly overlap at ca. 2640–2630 Ma. The close spatial and temporal relationship between gold
mineralization and felsic to intermediate magmatism at Jundee–Nimary also raises the possibility of a genetic link between
hydrothermal and igneous activity. However, additional work is required to establish a firm connection. Current research on
lode-gold mineralization in Archean, Paleozoic and Phanerozoic terranes suggests a model which postulates that these deposits
formed during transpressional to compressional deformation in accretionary and collisional orogens and that their formation
is intimately related to orogenic processes. Consequently, mineralization and regional metamorphism are expected to be diachronous,
as terranes are accreted and the front of orogenesis migrates. Consideration of the new data presented in this paper in conjunction
with previously published dates supports the hypothesis that gold mineralization, along with regional metamorphism, was generally
diachronous from northeast to southwest across the Yilgarn Craton, over a period of approximately 40 million years from ca.
2680–2660 Ma to ca. 2640–2630 Ma. This is directly analogous to the accepted model for the timing of orogenic lode-gold mineralization
in other provinces and therefore provides further support for a unified model for this style of deposit through geological
time.
Received: 17 March 2000 / Accepted: 8 September 2000 相似文献
102.
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105.
Spatial and temporal patterns of the infaunal community near a major ocean outfall in Southern California 总被引:1,自引:0,他引:1
D. R. Diener S. C. Fuller A. Lissner C. I. Haydock D. Maurer G. Robertson T. Gerlinger 《Marine pollution bulletin》1995,30(12):861-878
Effects of waste water discharge from a major ocean outfall in Southern California to the benthic infaunal community were examined during a 5-year monitoring programme. Natural features, primarily water depth, accounted for 82% of the variability in the infaunal community, while discharge-related effects represented less than 8% of the variability. The area immediately adjacent to the diffuser had the strongest outfall effects. Infaunal abundance showed a pattern of enhancement centred at the outfall. Diversity was also high, indicating that the area was not characterized by a degraded community. 相似文献
106.
Four years of detailed ground-water monitoring at a newly installed, seasonal-use, domestic septic system located on poorly buffered (CaCO3 equivalent content ≤ 1.6 wt.%) lacustrine silt, has revealed the development of an acidic ground-water plume. Acid, generated by the partial oxidation of effluent NH4+ dissolved organic carbon (DOC), and possibly sulfide minerals present in the sediment, has resulted in a distal plume core zone with pH values in the range of 4.4 to 5.0. The acidic zone, where NH4+ does, however, persist (> 2 mg/1, as N) and where DOC remains elevated (6–13 mg/1), is associated with high average concentrations of the trace metals Fe (4.7 mg/1), Al (1.9 mg/1), and Mn (3.6 mg/1). Attenuation of nitrogen along the plume core flowpath is indicated by a decrease in the N/ Cl− ratio from an effluent value of 1.7, to a plume value of only 0.5 after 4 m of subsurface flow. Increased SO42− levels observed in the zone of N depletion suggest that attenuation can be at least partly attributed to reduction of plume NO3− by oxidation of reduced S present in the sediment. PO43− has not migrated significantly beyond the infiltration bed gravel layer, demonstrating that PO43− mobility is limited in these sediments (retardation factor > 10). 相似文献
107.
William A. Robertson 《Pure and Applied Geophysics》1964,59(1):93-99
Summary Directions of natural remanent magnetization aftermagnetic cleaning of specimens from monzonite porphyry at Milton are given. Thermal and alternating magnetic field stability tests indicate that the resultant direction is that of the earth's magnetic field at the time of cooling. Comprison of the pole position calculated from this result with other pole positions from rocks of known age confirms the probable Permian age of the intrusion and the wide divergence of Australian from European and North American pole positions of this age. 相似文献
108.
Chathura Wickramasinghe Luke Wallace Karin Reinke Simon Jones 《International Journal of Digital Earth》2020,13(4):457-473
ABSTRACTThe AHI-FSA (Advanced Himawari Imager - Fire Surveillance Algorithm) is a recently developed algorithm designed to support wildfire surveillance and mapping using the geostationary Himawari-8 satellite. At present, the AHI-FSA algorithm has only been tested on a number of case study fires in Western Australia. Initial results demonstrate potential as a wildfire surveillance algorithm providing high frequency (every 10 minutes), multi-resolution fire-line detections. This paper intercompares AHI-FSA across the Northern Territory of Australia (1.4 million km2) over a ten-day period with the well-established fire products from LEO (Low Earth Orbiting) satellites: MODIS (Moderate Resolution Imaging Spectroradiometer) and VIIRS (Visible Infrared Imaging Radiometer Suite). This paper also discusses the difficulties and solutions when comparing high temporal frequency fire products with existing low temporal resolution LEO satellite products. The results indicate that the multi-resolution approach developed for AHI-FSA is successful in mapping fire activity at 500?m. When compared to the MODIS, daily AHI-FSA omission error was only 7%. High temporal frequency data also results in AHI-FSA observing fires, at times, three hours before the MODIS overpass with much-enhanced detail on fire movement. 相似文献
109.
110.
Seven piston cores, 7–16 m long, taken between the Kuril Islands and Emperor Seamounts, have been dated using radiolarian and diatom extinction levels and correlated using volcanic ash layers. The average rate of deposition in the cores decreases from 6 cm/1000 years near the Kuril Trench to about 3.5 cm/1000 years near the seamounts. Dispersed volcanic ash is the main constituent of the cores and it comprises up to 80% of the sediments. The percentage of the ash in the sediments decreases eastward from the Kuril Islands as the rates of deposition decrease.The total thickness of the sediments in the same latitudinal belt also decreases eastward. The thickness of the sediment inferred from seismic data near the Kuril trench is about 600 m and rates of deposition are approximately 6 cm/1000 years in the Pleistocene cores. Sediment thickness near the seamounts is about 300 m, and rates of deposition are approximately 3 cm/1000 years in the Pleistocene cores. Extrapolated rates of deposition in these cores suggest that the age of the base of the sediment to the east of the Kurils is only about 10 m.y.The anomalously young age for the base of the sediments obtained by extrapolation of an assumed constant rate of deposition can be explained by Deep Sea Drilling Project data from the northwest Pacific. The sediment thickness at DSDP site 192 east of Kamchatka includes sediments from all the Cenozoic epochs except the Paleocene. Rates of deposition of sediment younger than Middle Miocene are an order of magnitude higher than those prior to this time. At DSDP sites east of Japan, either Late Miocene sediments lie directly on the basement, or sediments older than Late Miocene are very thin. Post-Middle Miocene sediments are composed primarily of glass shards. Thus, about 90% of the total thickness of sediments in the northwest Pacific is composed of sediments younger than Middle Miocene with volcanic ash as the main constituent. The volcanic ash results from the present phase of explosive volcanic activity which began in the Late Miocene in the northwest Pacific volcanic arcs. 相似文献