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51.
Pramila Kumari Misra Sagarika Panigrahi P. Somasundaran 《International Journal of Mineral Processing》2006,80(2-4):229-237
The floatability of silica has been determined by adsorbing various concentrations of a series of polyoxyethylated nonyl and octyl alkyl phenols of varying oxyethylene units (10–40 units) to investigate the role of adsorbed layer. It is seen that the floatability of silica increases with increase in concentration till a maximum of 90% in premicellar region and then decrease to minimum of 40–45% in all cases in spite of the significant differences in adsorption densities. Zeta potential measurement reveals that a thin oxyethylene layer is formed at silica–water interface masking silica surface (Pramila K. Misra, P. Somasundaran, J. Surf. Deterg., Vol. 7, 2004, 373). This layer with oxyethylene units lying on silica surface and alkyl chain dangling to the bulk solution provides the same extent of hydrophobicity. The decrease in flotation recovery has been attributed to increase in the solvent hydrophobicity due to formation of premicellar aggregates and micelles. 相似文献
52.
This paper investigates the evolution of thrust wedges with concomitant surface erosion, and its bearing on the exhumation
processes in orogenic belts. We performed sandbox experiments, simulating syn-orogenic erosion on forelandward sloping surfaces
(∼4°). Experiments show that the erosion process has a significant control on the progression of frontal thrusts. In case
of no-erosion condition, wedges with high basal friction develop frontal thrusts with strongly increasing spacing. In contrast,
for the same basal friction the thrusts show uniform spacing as the wedge development involves concomitant surface erosion.
On the other hand, the erosion promotes reactivation of hinterland thrusts in wedges with low basal friction. We show that
erosion-assisted thrust reactivation is the principal mechanism for exhumation of deeper level materials in orogens. Efficiency
of this mechanism is largely controlled by basal friction. The exhumation of deeper level materials is limited, and occurs
within a narrow, sub-vertical zone in the extreme hinterland when the basal friction is high (μb = 0.46). In contrast, the process is quite effective in wedges with low basal friction (μb =0.36), resulting in exhumation along gently dipping foreland-vergent thrusts as well as along thrusts, subsequently rotated
into steep attitude. The zone of exhumation also shifts in the foreland direction in the course of horizontal movement. Consequently,
deeper level materials cover a large area of the elevated part of the wedge. 相似文献
53.
Pradeep Srivastava Surendra S. Bhakuni Khayingshing Luirei Dileep K. Misra 《第四纪科学杂志》2009,24(2):175-188
Morphological and sedimentary records at the exit of Brahmaputra River at Pasighat in the NE Himalaya inform about the climate–tectonic interplay during the past ca. 15 ka. The geomorphology of the area comprises (1) fan terrace T3, (2) a high‐angle fan (3) terrace T2, (4) terrace T1 and (5) a low‐angle fan. Geomorphic consideration suggests that the fan terrace T3 and high‐angle fans are the oldest units and were coeval. The low‐angle fan is the youngest geomorphic unit. Sedimentological studies and optically stimulated luminescence chronology suggest that (i) fan terrace T3 formed between 13 and 10.5 ka and comprised multiple events of debris flows separated by the aggradation as channel bars in a braided river environment; (ii) the high‐angle fan formed during 15–10 ka and comprises channel bar aggradation in braided river conditions; (iii) terrace T2 formed during 10–8 ka due to aggradation in a braided channel environment with lesser events of debris flows; (iv) terrace T1 formed during <7 and 3 ka took place as bars of the braided river. Sudden coarsening of the sediment indicated a tectonic rejuvenation in the provenance region between 7 and 3 ka; and (v) the low‐angle fans dated to <3 ka formed due to aggradation in a small tributary joining the Brahmaputra River. This implies a phase when the main channel of the Brahmaputra did not flood regularly and the tributaries were actively aggrading. The sedimentation style and incision of these geomorphic units responded to contemporary climatic changes and uplift in the Siwalik range along the Himalayan Frontal Fault. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
54.
The Lower Ordovician, Upper Knox Group rocks (the Kingsport and Mascot formations) in the Copper Ridge district consist predominantly of fine-grained dolostones, medium and coarser grained dolostones, and limestones. Dolomite crystals of medium and coarser grained dolostones show up to eight cathodoluminescent zones of variable width and intensity. Electron microprobe analyses indicate that the zoning is related to variation in Fe/Mn ratios, the brighter luminescent zones corresponding to lower ratios. Superposed on this growth zoning is a compositional zoning characterized by a general increase in Fe from core to rim of individual dolomite crystals.Field and petrographic studies (Churnet, 1979; Churnet et al., 1981) indicate that the fine-grained dolostones formed in supratidal to upper intratidal environments, whereas the precursor lime muds of the limestones as well as of the medium and coarser grained dolostones formed in shallow subtidal to lower intertidal environments. The large areal extent of the dolostones must have required a regionally abundant source of Mg such as marine water. Yet, both limestones and dolostones have low Na and Sr contents suggestive of their formation in solutions more dilute than normal marine water. It is proposed that the fine-grained dolostones formed by aggradation of initially very fine-grained dolostones in presence of fresh water, and that the limestones stabilized and the medium and coarser grained dolostones formed in environments of mixed marine and fresh waters. Considered in the light of ordering of partition coefficients, such a mixing model can account for the observed correlation pattern of trace elements (especially, SMn and SrFe) as well as the Fe distribution in the zoned dolomite crystals. Variation of the partition coefficient of Mn due to fluctuations in the relative proportions of fresh and marine waters in the diagenetic solution may explain the different Fe/Mn ratios observed in the growth zones (luminescence bands) of zoned dolomite crystals. 相似文献
55.
Sr90 Radiotracer diffusion studies have been carried out on crystals of orthoclase and microcline using an ion implantation method. The activation energies are consistent with calculations based on mineral age data. 相似文献
56.
Pure and Applied Geophysics - Deflection and bending moments of a thin isotropic rectangular plate, having its edges simply supported and maintained at zero temperature, have been investigated in... 相似文献
57.
58.
Mruganka K. Panigrahi Brendan R. Bream Kula C. Misra Rajesh K. Naik 《Mineralium Deposita》2004,39(5-6):670-677
The Malanjkhand copper–molybdenum deposit in the Bhandara Craton, Central India, is hosted by a granite complex which consists of regionally dominant grey granitoid and pink granitoid confined to the mineralized zone. New SHRIMP RG data on zircons from both granite types are inferred to have crystallized during the same magmatic pulse at ca 2.48 Ga. The discrepancy between zircon age and earlier obtained Rb–Sr whole-rock age is attributed to modification of the Rb–Sr system by hydrothermal overprint. Similarity in petrographic features and chemical affinity in combination with identical age strongly indicate that the pink granite is the hydrothermally altered variety (microclinization and silicification) of the grey granite. The spatially associated, main Cu–Mo mineralization event at Malankhand appears to be broadly contemporaneous with and genetically related to the emplacement of the host granitoids at about 2.48 Ga. 相似文献
59.
Prediction of Arsenic in Bedrock Derived Stream Sediments at a Gold Mine Site Under Conditions of Sparse Data 总被引:2,自引:0,他引:2
Navin K. C. Twarakavi Debasmita Misra Sukumar Bandopadhyay 《Natural Resources Research》2006,15(1):15-26
Arsenic is often present in gold mining areas. The high sensitivity of arsenic to biogeochemical conditions may lead to catastrophic
consequences through contamination of resources such as ground water. Therefore, it is critical to understand the spatial
occurrence of arsenic across a given site. Previous studies using traditional pattern recognition techniques such as neural
networks and kriging have not been entirely successful in predicting arsenic concentrations across a gold mining area. The
methods used in this paper are the support vector machines (SVM) and robust least-square support vector machines (robust LS-SVM).
The two techniques were used to predict arsenic concentrations in the sediments of Circle City, Alaska, using the gold concentration
distribution present within the sediments. The analysis of the results shows an improved performance and better predictive
capabilities of SVM and robust LS-SVM than that of the neural networks and kriging techniques. The robust LS-SVM performed
better than the SVM. The performance of the SVM was affected by outliers. The removal of the outliers from the data set and
application of SVM showed improved results. 相似文献
60.