Sulfur and carbon isotope compositions in the stratiform Zn-Pb-Cu sulfide deposits of the Rajpura-Dariba belt,Rajasthan, NW India: A model of ore genesis     

M. Deb 《Mineralium Deposita》1986,21(4):313-321

The sulfur isotope composition of 86 sulfide minerals from the Middle Proterozoic, metamorphosed, stratiform, sediment-hosted Zn-Pb-CU sulfide deposits of Dariba and Sindeswar Kalan located within the Rajpura-Dariba belt in Rajasthan, NW India, have been determined. In addition, 16 carbonaceous and 2 carbonate rock samples from the ore zone have been analyzed for their C_tot and C_org contents and carbon isotope compositions. The sulfur isotope compositions range from 9.1 to –6.7 (mean value of 1.9). Increasing ³⁴S values stratigraphically upward are observed, particularly for pyrite and pyrrhotite suggesting a syngenetic origin for the sulfur. No marked lateral isotopic variations or isotopic variation in minerals from successive laminae in banded ore samples occur. Fractionation of sulfur isotopes between coexisting sulfides suggests that the original isotopic pattern was basically preserved during the amphibolite-facies metamorphism suffered by the deposits. C_org in carbonaceous rocks ranges 0.5–9.3 wt%, with ¹³C values between –21 and –31 (mean of –25.4) in keeping with the biogenic derivation of the carbon. Recrystallized dolostones have ¹³C values close to –14.4Geological evidence and isotopic features are consistant with the following genetic scheme: (a) base-metal ores along the belt formed from geothermal emanations carrying H₂S, produced by the chemical reduction of seawater sulfates and leaching of mafic volcanics, in a semiclosed (with respect to SO₄), shallow-water, rift-related basin with high biological activity; (b) pyrite and pyrrhotite formed diagenetically by bacterial reduction of sulfate in pore seawater in a system open to H₂S, thus bringing about the gradual enrichment of ³⁴S in these minerals stratigraphically upward; and (c) northward in the belt, at Sindeswar Kalan, the basin of ore deposition was relatively more open.  相似文献   

Precambrian stromatolite and other structures in the Rajpura-Dariba polymetallic ore deposit,Rajasthan, India     

M. Deb  D. M. Banerjee  A. K. Bhattacharya 《Mineralium Deposita》1978,13(1):1-9

Intimate association of 2 billion years old stromatolite with pyritic lead-zinc ores in the Precambrian polymetallic deposit at Rajpura-Dariba in Rajasthan, which hitherto remained unreported, provides an additional documentation of the syn(-dia)-genetic mineralization. The growth form and petrography of the stromatolite structure have been described and an explanation sought regarding the concentration of sulfides along the siliceous and carbonaceous laminations, as well as in the intercolumnar regions. Consideration of the geologic features noted in the mineralized zone and surrounding region suggests that the stratiform ores were deposited in a near-shore shallow marine environment, developed on basement highs and associated with euxinic conditions. Later, the ores were metamorphosed under conditions reaching upto amphibolite facies during a three-stage deformational history of their enclosing rocks. Some salient features of the secondary structures in the ores have been discussed in relation to this deformation history.  相似文献   

Mapping of environs of Dharavi slums of Greater Bombay for site suitability using enhanced Landsat thematic mapper (TM) imagery     

V. Raghavswamy  N. C. Gautam  J. Krishnamurthy 《Journal of the Indian Society of Remote Sensing》1989,17(1):49-54

Slums are universal and a ubiquitous part of the urban landscape. Dharavi, the biggest slum in the whole of Greater Bombay, encompasses 4.0 sq.km. of reclaimed land with 3.50 lakh inhabitants and 75,000 hutments. Majority of the slums of Indian cities, being structurally small with high density of dwellings and uniform building material, seldom give subtle ’spectral signature’ on the satellite imagery. Here, an attempt has been made to map by visual techniques the land use of Dharavi and environs of 20 sq.km area, using optically enhanced Landsat (TM) FCC of January, 1986, on 1:25,000 sale, The study has clearly brought out the land use details, the areas undergoing reclamation, and those susceptible to hazards like floods and marine erosion. A few alternate sites, based on geomorphic attributes are suggested for resettlement of Dharavislum and their areas are also quantified. The results of the present work is a part of the project study completed for a larger area covering 150sq. kms.  相似文献   

Study of Strain Rate and Thermal Damage of Dholpur Sandstone at Elevated Temperature   总被引：1，自引：0，他引：1  

P. K. Gautam  A. K. Verma  M. K. Jha  K. Sarkar  T. N. Singh  R. K. Bajpai 《Rock Mechanics and Rock Engineering》2016,49(9):3805-3815

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Numerical Analysis of Sill and Crown Pillar Stability for Multilevel Cut and Fill Stopes in Different Geomining Conditions     

Hemant Kumar  Debasis Deb  Debashish Chakravarty 《Geotechnical and Geological Engineering》2016,34(2):529-549

A steeply dipping orebody, having decreasing width with depth has been modeled considering horizontal cut and fill method of stoping at four different depth levels. The focus of the study is to identify and understand the behavior of crown and sill pillars in terms of varying stress and geo-mining conditions without reinforcement using finite element method. Analysis of stresses, displacements and extent of yield zones around the excavation is carried out by varying the rock mass conditions such as geological strength index, uniaxial compressive strength (UCS or σ _ci), modulus of elasticity (E), and thickness of crown and sill pillars (T). These analyses have been conducted based on 135 non-linear numerical models considering Drucker–Prager material model in plane strain condition. Results of the study provide valuable insight into the stress concentration factors of the pillars highlighting stress distributions, roof convergence, yield zones and support requirements. Finally, it suggests the optimum thickness of crown and sill pillar with varying thickness of orebody.  相似文献   

On convective entrainment in a mass flux cumulus parameterization     

S. K. Deb  H. C. Upadhyaya  J. Y. Grandpeix  O. P. Sharma 《Meteorology and Atmospheric Physics》2006,94(1-4):145-152

Summary A new entrainment/detrainment formulation in the Tiedtke’s mass flux cumulus parameterization is discussed here. Apart from validating it with observations both in one and three dimensional cases, it is also evaluated in the light of the results from the original Tiedtke scheme and another mass flux scheme due to Emanuel. The proposed analytical profiles of entrainment and detrainment, easier to implement in any mass flux scheme, give reasonable results in GCM experiments.  相似文献   

Nonlinear analysis of multilayer extensible geosynthetic-reinforced granular bed on soft soil     

Kousik Deb  S. Chandra  P. K. Basudhar 《Geotechnical and Geological Engineering》2007,25(1):11-23

The paper presents a model for the analysis of granular foundation beds reinforced with several geosynthetic layers. Such reinforced granular beds are often placed on soft soil strata for an efficient and economical transfer of superstructure load. The granular bed is modeled by the Pasternak shear layer and the geosynthetic reinforcement layers by stretched rough elastic membranes. The soft soil is represented by a series of nonlinear springs. The reinforcement has been considered to be extensible and it is assumed that the deformation at the interface of the reinforcements and soil are same. The nonlinear behavior of the granular bed and the soft soil is considered. Plane strain conditions are considered for the loading and reinforced foundation soil system. An iterative finite difference scheme is applied for obtaining the solution and results are presented in nondimensional form. The results from the proposed model are compared to the results obtained for multilayer inextensible geosynthetic reinforcement system. Significant reduction in the settlement has been observed when the number of reinforcement layer is increased. In case of inextensible reinforcements as the number of reinforcement layer is increased the settlement is decreased with a decreasing rate, but in case of extensible reinforcement the reduction rate is almost constant. Nonlinear behavior of the soft soil decreases as number of reinforcement layer is increased. The effect of the stiffness of the geosynthetic layer on the settlement response becomes insignificant for multilayer reinforced system, but the mobilized tension in the reinforcement layers increases as the stiffness of the geosynthetic layers increases.  相似文献   

Numerical Analysis of Multi Layer Geosynthetic-Reinforced Granular Bed over Soft Fill     

Kousik Deb  N. Sivakugan  Sarvesh Chandra  P. K. Basudhar 《Geotechnical and Geological Engineering》2007,25(6):639-646

In this paper, considering the plain strain conditions, a numerical study has been conducted to investigate the behavior of multi layer geosynthetic-reinforced granular bed overlying a soft soil using the Fast Lagrangian Analysis of Continua (FLAC) program. The granular fill, soft soil, and geosynthetic reinforcements are considered as linear elastic materials. The geosynthetic reinforcements are modeled as cable elements fully bonded with the surrounding soil, thus neglecting any slip. The results obtained from the present investigation showed very close agreement when compared with the results of finite element analysis and lumped parameter modeling. The distribution of vertical, lateral and shear stresses in the soil are greatly affected as the number of reinforcement layers is increased. If the tensile stiffness of geosynthetic layers increases and its value is no more than 4,000–5,000 kN/m, the settlement of the reinforced foundation decreases significantly. The reduction in settlement is insignificant when the tensile strength of the geosynthetics exceed the above value.  相似文献   

A nonlinear polar coordinate shallow water model for tsunami computation along North Sumatra and Penang Island     

Gauranga Deb Roy  Md. Fazlul Karim  Ahmad Izani M. Ismail 《Continental Shelf Research》2007

A nonlinear shallow water model in cylindrical polar coordinate system is developed, using an explicit finite difference scheme with a very fine resolution, to compute different aspects of tsunami at North Sumatra and the adjacent island Simeulue in Indonesia, and the Penang Island in Peninsular Malaysia. The pole of the frame is placed on the mainland of Penang (100.5°E) and the model area extends up to the west of Sumatra (87.5°E). The model is applied to simulate the propagation of tsunami wave towards North Sumatra, Simeulue and Penang Islands associated with Indonesian tsunami of 26 December 2004. The model is also applied to compute water levels along the coastal belts of those islands. Computed and observed water level data are found to be in good agreement and North Sumatra is found to be vulnerable for very high surges. The computed and observed arrival times of high surges are also in reasonable agreement everywhere. Further studies are carried out to investigate the effect of convective terms and it is found that their effects are insignificant in tsunami propagation and weakly significant for wave amplitude very near to the coast.  相似文献   

Water Quality Monitoring of Tropical Ponds: Location and Depth Effect in Two Case Studies     

Gautam Mukhopadhyay  Debasis Mondal  Pinaki Biswas  Anjana Dewanji 《洁净——土壤、空气、水》2004,32(2):138-148

The variability in water chemistry of samples taken on a monthly basis (March 1999 to February 2000) from two shallow tropical ponds was studied. The effect of location and pond depth on water chemistry was also examined. The study demonstrated that intraannual variability in nutrient concentration is high. Thus, a high annual sampling frequency is required to provide representative annual mean water quality data. Routine monitoring during the monsoons is important for studies on dissolved oxygen and macrophyte growth. Significant differences were found between the topmost and bottommost points for samples of dissolved oxygen collected from the deepest part of both ponds. For nutrient analysis (nitrogen and phosphorus), sample from any location was found to be representative of the whole pond.  相似文献