Lateritisation as a possible contributor to gold placers in Nilambur Valley, southwest India

Panning for placer gold in the river beds of Punna Puzha and Chaliyar Puzha in the Nilambur Valley, southwest India, has been in vogue among the local people for the last few centuries. The auriferous quartz veins and reefs associated with the Precambrian migmatitic gneisses of the region had been mined for several years. Of late, Au is also being recovered from the laterite matrix of gravels in the old river terraces and from the residual laterites overlying the gneisses. The size of Au nuggets associated with the laterites is much higher (0.5 mm) than that of the Au in vein quartz (0.2 mm) and the associated heavy minerals in the placers (0.2 mm). The Au nuggets show surface and internal textures characteristic of redeposition under low-temperature conditions. Our field and laboratory investigations suggest that dissolution, transport and redeposition of Au occurred in Nilambur concomitant with the lateritisation process.     

HF doppler observations on the occurrence of equatorial spread-F

HF doppler observations of the vertical drift velocity and group height of the 5.5 MHz plasma frequency level of the post-sunset bottomside F-region obtained on a fewESF (equatorial spread-F) and non-ESF days at Trivandrum are presented. The results show that on the non-ESF days, the maximum group height attained is about 400 km and the maximum velocity is less than 30 m/sec. On theESF days, however, the corresponding values are found to be in the range of 400–650 km and 30–50 m/sec. TheESF onset is found to be significantly delayed relative to the velocity peak indicating that it is more closely linked to the layer height than to the drift velocity.     

Microscale Response of Sediment Variables to Benthic Disturbance in the Central Indian Ocean Basin

The response of sediment bacteria and biochemical variables to benthic disturbance was investigated in the Central Indian Ocean Basin from cores at nine stations. Generally, bacterial density and biochemical variables declined vertically with depth in the upper layers of the cores. Mechanical disturbance caused by a hydraulic disturber brought about a substantial decrease in total bacterial numbers. However, the numbers of retrievable bacteria increased by two orders of magnitude. The biochemical parameters decreased in quantity with a shift in the linear relationship. The data suggest that abiotic artifacts will directly affect the biomass and biochemistry of the sediment.     

Cadmium speciation and transport in the blood of the bivalve Mytilus edulis.

Cadmium (Cd) speciation in the blood plasma of Mytilus edulis was investigated using the metal speciation model MINTEQA2. In the presence of inorganic ions alone, Cd-chloro complexes dominated the speciation (97% of total Cd), with 3% as Cd2+. Inclusion of a novel Cd-binding histidine-rich glycoprotein (HRG) purified from mussel blood plasma decreased the contribution of chloro-complexes to 11.9%, with 86.8% of the Cd bound to the HRG and 1.3% present as Cd2+. Cd transfer from the blood plasma to the kidneys in vivo was studied by injecting 109Cd (both with and without additional chelation) into mussels. Oxine and EDTA complexed a significant amount of blood-borne Cd (23.7% Cd Oxine; 57.1% CdEDTA). In the presence of each chelator, plasma retained significantly more Cd, although there was no significant difference in Cd uptake by tissues (kidney, gill-mantle, and remaining viscera).     

Global electric circuit parameters and their variability observed over Maitri,Antarctica

The global component of fairweather electricity is subject to special attention to watch the solar-terrestrial effects and secular changes in climate. It is generally considered that the diurnal variation of atmospheric electricity parameters, if they are not following the Carnegie pattern, are not representative of the global thunderstorm activity. Some of the results obtained from Maitri (70°45′54″S, 11°44′03″), are discussed here in context with global thunderstorm activity and space weather influences. The diurnal pattern of the Potential Gradient and current density strongly deviate from the Carnegie curve. We have showed that this deviation is not due to the local electrical influence but due to the global thunderstorm activity. During fairweather condition the parameters are representing the global thunderstorm activity and to some extent they respond to the upper atmospheric electro dynamic phenomenon. The mean value of the potential gradient (77.7 V/m) and current density (2.13 pA/m²) well below the expected global mean but close to the value reported from the same location and season in the past years. The mean conductivity, 3.34 × 10⁻¹⁴ mhom⁻¹, is slightly at higher side and they exhibit a different diurnal trend comparing to the past measurements at this location.     

Time-dependent plume front positioning and its dynamics coupled with seasonal river efflux

Ocean Dynamics - The time-dependent plume front positioning with respect to different tidal phases and its dynamics coupled with seasonal river efflux on the shelf off Kochi, southwest coast of...     

Landslide susceptibility assessment using Information Value Method in parts of the Darjeeling Himalayas

Landslide susceptibility is the likelihood of a landslide occurrence in an area predicted on the basis of local terrain conditions. Since last few years, researchers have attempted to analyse the probability of landslide occurrences and introduced different methods of landslide susceptibility assessment. The objective of this paper is to assess the landslide susceptibility in parts of the Darjeeling Himalayas using a relatively simple bivariate statistical technique. Seven factor layers with 24 categories, responsible for landslide occurrences in this area, are prepared from Cartosat and Resourcesat — 1 LISS-IV MX data. Each category was given a weight using the Information Value Method. Weighted sum of these values were used to prepare a landslide susceptibility map. The result shows that 8% area was predicted for high, 32% for moderate and remaining 60% for low landslide susceptibility zones. The high value (0.89) of the area under the receiver operating characteristic curve showed the high accuracy of the prediction model.     

Surface complexation modeling of Uranium(VI) sorption on quartz in the presence and absence of alkaline earth metals

Surface complexation models (SCMs) are widely utilized as a tool to study the mobility of radionuclide to the environment. In this study, two SCMs, electrostatic (ES) and non-electrostatic (NES) models are employed in order to simulate the sorption behavior of U(VI) on quartz in the absence of Mg, Ca, and Sr and ES model in the presence of alkaline earth metals. The surface reaction constants (log K) for ES and NES models were fitted to experimental data by coupling PEST with PHREEQC. The SCM prediction of U(VI) sorption on quartz in the absence of alkaline earth metals is in good agreement with the experimental data in the pH range 6.5–9. The estimated log K values are sensitive to both ES and NES model calculations. In U(VI)-Mg-quartz, U(VI)-Ca-quartz, and U(VI)-Sr-quartz systems, only the ES model shows the general trend of the experimental data. The estimated log K values are sensitive with respect to the surface reactions. Hence, the ES model is more suitable for model calculations of the U(VI)-Mg-quartz, U(VI)-Ca-quartz, and U(VI)-Sr-quartz systems.     

Mobilization of trace metals in a tropical turbid estuary influenced by a monsoon season

The selective removal of trace metals by suspended matter in high turbidity zones plays a major role in the fluvial transport of terrigenous metals to the marine environment. The seasonal longitudinal variability of trace elements (Cu, Zn, Cd, Ni, Pb, Fe, and Mn) in Cochin estuary, a tropical positive estuary, was studied and the results were compared with the prevailing situation in other subtropical waterways. The hydrodynamical features showed increasing turbidity downstream with increasing salinities during both the seasons. In contrast with the temperate estuaries where the development of turbidity maxima causes the removal of metals, the estuaries of tropics modify the fluvial transport of metals by the way of redistribution between the dissolved and particulate fractions in the intermediate salinities. In Cochin estuary, the distributional features of trace metals are primarily influenced by the variations in salinities and river discharges. Consequently, this gives rise to two different types of distributional patterns: (1) during premonsoon, the estuarine reactivity is more pronounced and hence, mid-estuarine solubilization of the particulate metal appears to play a prominent role in controlling the fluxes of trace metals studied and (2) but during monsoon, the hydrological conditions influence the downstream transport of the metals more by physical dilution than chemical reactivity.     

Influence of flow velocity on conservative solute transport in sets of parallel fractures with fracture skin

Analysis of contaminant transport through fractured crystalline rocks has received considerable attention, particularly with regard to subsurface nuclear waste repositories. Most of the studies have employed the dual continuum approach, with the fractures and the rock matrix as the two continuums, assuming that fractures control the overall conductivity of the rock and the porous matrix just provides storage. However, field observations of rock fractures have shown that the real situation can be very complex. Based on some recent investigations, it has been reported that the portion of the rock matrix adjacent to many open fractures is physically and chemically altered. These alterations, referred to as the fracture skin, can have different sorption and diffusion properties compared to those of the undisturbed rock matrix and this may influence the transport of solutes through such formations. In the present study, a numerical model is developed to simulate conservative solute transport in a fractured crystalline rock formation using the triple continuum approach ?? with the fracture, fracture skin and the rock matrix as the three continuums. The model is solved using a fully implicit finite difference scheme. Contaminant migration in the fractured formation with and without skin has been simulated. It is observed that contaminant penetration along the fracture is enhanced at large flow velocities. The effect of flow velocity on conservative solute transport is investigated for different fracture apertures and fracture skin thicknesses. The influence of flow velocity on contaminant transport is demonstrated to be more with change in fracture aperture than with change in skin thickness.