Weathering of ilmenite from Chavara deposit and its comparison with Manavalakurichi placer ilmenite,southwestern India     

Ajith G. Nair  D.S. Suresh Babu  K.T. Damodaran  R. Shankar  C.N. Prabhu 《Journal of Asian Earth Sciences》2009,34(2):115-122

The magnetic fractions of ilmenite from the beach placer deposit of Chavara, southwest India have been studied for mineralogical and chemical composition to assess the range of their physical and chemical variations with weathering. Chavara deposit represents a highly weathered and relatively homogenous concentration. Significant variation in composition has been documented with alteration. The most magnetic of the fractions of ilmenite, separated at 0.15 Å, and with a susceptibility of 3.2 × 10^?6 m³ kg^?1, indicates the presence of haematite–ilmenite intergrowth. An iron-poor, titanium-rich component of the ilmenite ore has been identified from among the magnetic fractions of the Chavara ilmenite albeit with an undesirably high Nb₂O₅ (0.28%), Cr₂O₃ (0.23%) and Th (149 ppm) contents. The ilmenite from Chavara is compared with that from the nearby Manavalakurichi deposit of similar geological setting and provenance. The lower ferrous iron oxide (2.32–14.22%) and higher TiO₂ (56.31–66.45%) contents highlight the advanced state of alteration of Chavara. This is also evidenced by the relatively higher Fe³⁺/Fe²⁺ ratio compared to Manavalakurichi ilmenite. In fact, the ilmenite has significantly been converted to pseudorutile/leucoxene.  相似文献   

Understanding the Spatial Variability of Chlorophyll a and Total Suspended Matter Distribution Along the Southwest Bay of Bengal Using In-Situ and OCM-2 & MODIS-Aqua Measurements     

D. Poornima  R. Shanthi  S. Raja  G. Vijayabaskara Sethubathi  T. Thangaradjou  T. Balasubramanian  K. N. Babu  A. K. Shukla 《Journal of the Indian Society of Remote Sensing》2013,41(3):651-662

Spatial and temporal distribution of chlorophyll a (chl a) and Total Suspended Matter (TSM) and inter comparison of Ocean Color Monitor-2 (OCM-2) and Moderate Resolution Imaging Spectro-radiometer (MODIS-Aqua) derived chlorophyll a and TSM was made along the southwest Bay of Bengal (BoB). The in-situ chl a and TSM concentration measured during different seasons were ranged from 0.09 to 10.63 μgl^?1 and 11.04–43.75 mgl^?1 respectively. OCM-2 and MODIS derived chl a showed the maximum (6–8 μgl^?1) at nearshore waters and the minimum (0–1 μgl^?1) along the offshore waters. OCM-2 derived TSM imageries showed the maximum (50–60 mgl^?1) along the nearshore waters of Palk Strait and the moderate concentration (2–5 mgl^?1) was observed in the offshore waters. MODIS derived minimum TSM concentration (13.244 mgl^?1) was recorded along the offshore waters, while the maximum concentration of 15.78 mgl^?1 was found along the Kodiakarai region. The inter-comparison of OCM-2 and MODIS chl a data (R ² ?=?0.549, n?=?49, p?<?0.001, SEE?=?±0.117) indicate that MODIS data overestimates chl a concentration in the nearshore waters of the southern BoB compared to the OCM-2. The correlation between OCM-2 and MODIS-Aqua TSM data (R ² ?=?0.508, N?=?53, P?<?0.001 and SEE?=?±0.024) confirms that variation in the range of values measured by OCM-2 (2–60 mgl^?1) and the MODIS (13–16 mgl^?1) derived TSM values. Despite problems in range of measurements, persistent cloud cover etc., the launch of satellites like OCM-2 with relatively high spatial resolutions makes job easier and possible to monitor chl a distribution and sediment discharges on day to day basis in the southwest BoB.  相似文献   

Response of Vertically Loaded Pile in Clay: A Probabilistic Study     

Sumanta Haldar  G. L. Sivakumar Babu 《Geotechnical and Geological Engineering》2012,30(1):187-196

This study presents the response of a vertically loaded pile in undrained clay considering spatially distributed undrained shear strength. The probabilistic study is performed considering undrained shear strength as random variable and the analysis is conducted using random field theory. The inherent soil variability is considered as source of variability and the field is modeled as two dimensional non-Gaussian homogeneous random field. Random field is simulated using Cholesky decomposition technique within the finite difference program and Monte Carlo simulation approach is considered for the probabilistic analysis. The influence of variance and spatial correlation of undrained shear strength on the ultimate capacity as summation of ultimate skin friction and end bearing resistance of pile are examined. It is observed that the coefficient of variation and spatial correlation distance are the most important parameters that affect the pile ultimate capacity.  相似文献   

Study of terrestrial carbon flux by eddy covariance method in revegetated manganese mine spoil dump at Gumgaon,India     

Rajani Nair  Asha A. Juwarkar  Tushar Wanjari  S. K. Singh  T. Chakrabarti 《Climatic change》2011,106(4):609-619

The micrometeorological technique of eddy covariance is a powerful tool for characterizing the carbon (C) budget of terrestrial ecosystems. Eddy covariance method was used for estimating Net Ecosystem Exchange (NEE) of carbon dioxide between atmosphere and revegetated manganese mine spoil dump at Gumgaon, India. In this paper, we analyzed the diel CO₂ flux pattern and its response to various physical environmental conditions. The carbon balance of terrestrial ecosystems is particularly sensitive to climatic changes. Study of diel pattern of CO₂ flux showed that carbon uptake was dependent on sunlight. Effect of temperature and latent heat on the CO₂ flux showed that rate of CO₂ uptake increased proportionally, but later declined due to various factors like stomatal response, high evaporative demand, circadian rhythm and/or a combination of all three. Net ecosystem production of revegetated land was found to be 28.196 KgC/ha/day whereas average net carbon release by the ecosystem, through respiration was observed to be 5.433 KgC/ha/day. Thus, quantifying net carbon (C) storage in degraded land is a necessary step in the validation of carbon sequestration estimates and in assessing the possible role of these ecosystems in offsetting adverse impacts of fossil fuel emissions.  相似文献   

Environmental impact on groundwater of Maheshwaram Watershed,Ranga Reddy district,Andhra Pradesh     

D. Purushotham  A. Narsing Rao  M. Ravi Prakash  Shakeel Ahmed  G. Ashok Babu 《Journal of the Geological Society of India》2011,77(6):539-548

Maheshwaram watershed is situated in Ranga Reddy district of at a distance of about 30 km south of Hyderabad. The watershed has an area of 53 km² and has hard rock aquifers with semi-arid climate. The study area has been expanding at a fast pace and now has the distinction of being one of the fastest growing urban centers, facing the problem of groundwater depletion and quality deterioration due to the absence of perennial source of surface water and also due to over exploitation. Human activities involving industrial and agricultural development and the inadequate management of land and water resources have, directly or indirectly resulted in the degradation of environment viz. water and soil.  相似文献   

Paleoproterozoic quartz-pebble conglomerate type uranium mineralisation in Mankarhachua area,Angul district,Orissa     

Kalyan Chakrabarti  N. R. R. Ecka  B. Mishra  P. V. Ramesh Babu  P. S. Parihar 《Journal of the Geological Society of India》2011,77(5):443-449

Ground Radiometric survey of Paleoproterozoic pyritiferous quartz-pebble conglomerate (QPC) occurring to the north of Pallahara area led to the discovery of a QPC type uranium mineralisation near Mankarhachua village. Significant radioactivity is recorded in three sub-parallel uraniferous QPC horizons with metamorphosed pebbly to medium grained recrystallised massive sandstones. Detrital grains of uranothorite, thorite, radioactive allanite, monazite, zircon, minute uraninite grains in carbonaceous matter and thucolite contributes to the radioactive phases present in QPC matrix. Adsorbed U on limonite and goethite, secondary uranyl minerals in matrix, along bedding planes and fractures are commonly observed. This discovery has opened up a new horizon for future exploration for QPC type uranium mineralization in the area. The paper presents observations on geology, radioactivity, petrological and geochemical nature of the uraniferous QPC horizons.  相似文献   

Bastnaesite from Kanigiri granite, Prakasam district, Andhra Pradesh     

G. Nagendra Babu  M. Sai Baba  Mary K. Kumar  Yamuna Singh  P. V. Ramesh Babu  P. S. Parihar 《Journal of the Geological Society of India》2013,81(4):447-450

For the first time we report bastnaesite and hydroxyl bastnaesite (lanthanum cerium fluoro-carbonate) from the Kanigiri granite. The host granitoids are of A-type and vary in composition from quartz syenites to peralkaline granites. Rare metal and rare earth-bearing minerals identified by X-ray diffraction (XRD) studies in Kanigiri granite are bastnaesite and hydroxyl bastnaesite, besides columbite-tantalite, monazite, fergusonite, thorite and euxenite. Petromineralogical studies have also revealed the presence of bastnaesite. The presence of bastnaesite in Kanigiri granite suggests that the host felsic rocks may also form a potential source for light rare earth mineral, bastnaesite, apart from the already known rare-metal minerals.  相似文献   

Heavy mineral distribution and characterisation of ilmenite of Kayamkulam — thothapally Barrier Island, southwest coast of India     

Babu Nallusamy  Sinirani Babu  D. S. Suresh Babu 《Journal of the Geological Society of India》2013,81(1):129-140

Mineral concentration and ilmenite characterization of the Thothapally — Kayamkulam Barrier Island of the southern Kerala has been studied. 96.86% concentrations of heavy minerals are recorded in the surficial and core samples (4 m) in the southern Kayamkulam and northern Thothapally areas. The total heavy mineral content decreases with depth. The primary heavy mineral suite of the surficial and core samples consists of ilmenite, sillimanite, zircon, garnets, rutile, monazite and magnetite. Longshore current and onshore-offshore movements of sediment during the southwest monsoon are primarily responsible in sorting of the heavy minerals. TiO₂ content in ilmenite is significantly higher in the Kayamkulam core sediments than the surface samples. XRD analysis supports intensive weathering and alteration leading to the higher TiO₂ concentration. Higher percentage of ferric iron than ferrous iron in the core samples reveals that considerable weathering occurred under burial condition. SEM examination of ilmenite grains reveal the presence of solution pit, chemical leaching, corrosion and replacement textures, supporting the intense epigenetic alteration and weathering under subaerial condition and post-depositional changes by water-table condition.  相似文献   

Signature of potassium enrichment in granite of the Chitrial area, Nalgonda district, Andhra Pradesh: Inferences using its U, Th, K2O, Na2O, Rb, Ba and Sr contents     

H. S. Rajaraman  G. Nagendra Babu  S. J. Chavan  K. K. Achar  P. V. Ramesh Babu 《Journal of the Geological Society of India》2013,82(1):53-58

A medium tonnage unconformity proximal uranium deposit has been established at Chitrial by the Atomic Minerals Directorate in the Srisailam sub-basin. In this type of deposits, the association of uranium with potassic alteration (illitization) is well-documented. The present study is directed towards understanding such an association in the Chitrial area for which the uranium mineralized borehole core samples were collected and analyzed. It is observed that the average concentrations of K₂O, Na₂O, Rb, Ba and Sr in the granite of the Chitrial area are 5.35%, 1.78%, 252 ppm, 564 ppm and 52 ppm, respectively, and they show average critical elemental ratios of K/Rb, Ba/Rb and Rb/Sr as 191, 2.37 and 7.13, respectively. The granites show low K/Rb, low Rb/Ba and high Rb/Sr ratios compared to that of the average crust indicating its derivation from crustal source. The samples have higher values of uranium (av. 53 ppm), thorium (av. 66 ppm) and lead (av. 41 ppm). The U/Th ratio in the granite varies from 0.07 to 20.86 with an average of 1.68. They also exhibit high K₂O/Na₂O ratio typical of post-Archaean granite and very high values suggest the possibility of later potassium enrichment.  相似文献   

Fluoride-bearing groundwater in Gummanampadu Sub-basin, Guntur District, Andhra Pradesh, India   总被引：1，自引：0，他引：1  

N. Subba Rao  A. Subrahmanyam  G. Babu Rao 《Environmental Earth Sciences》2013,70(2):575-586

The functional factors responsible for fluoride (F^?)-bearing groundwater used for drinking as well as for cooking in the area of Gummanampadu Sub-basin, Guntur District, Andhra Pradesh, India are discussed. The study area is a part of an Archean Gneissic Complex, consisting of banded-biotite-hornblende-gneisses, over which the Proterozoic Cumbhum quartzites, shales, phyllites, and dolomitic limestones occur. The chemistry of groundwater is dominated by carbonates (HCO₃ ^? and CO₃ ^2?) at a higher pH. This results in a higher total alkalinity over total hardness, causing an excess alkalinity. Sodium ion is dominated among the cations (Ca²⁺, Mg²⁺, and K⁺). The concentration of F^? (2.1–3.7 mg/L) is higher than that of desirable national limit (1.2 mg/L) prescribed for drinking purpose. A significant positive correlation exists between F^? and pH as well as that between F^? and HCO₃ ^? + CO₃ ^2?. This indicates that the alkaline condition is the prime conducive factor for dissolving F^?-bearing minerals more effectively leading to a higher concentration of F^? in the groundwater. Furthermore, a positive chloro-alkaline index reflects the ion exchange, and an oversaturation with respect to CaCO₃ indicates the evaporation. In addition, a negative relation between the well depth and F^? shows the effect of solubility and/or leaching of salts in different depth levels. These factors regulate the concentration of F^? in the groundwater. On the other hand, a positive correlation of F^? with SO₄ ^2? as well as with K⁺ shows the human land use activities (namely, use of chemical fertilizers, disposal of domestic wastes, etc.), which add F^? to the groundwater. A significant number of the residents of the study area suffer from the health disorders related to fluorosis, which is a consequence of higher concentration of F^? in the drinking water. Thus, this study emphasizes the need for supply of safe drinking water, nutritional diet, rainwater-harvesting structures, and public education to realize “health for all” motto of World Health Organization.  相似文献