Animesh Mandal

Somatic embryogenesis of safflower: influence of auxin and ontogeny of somatic embryos

Influence of auxin type and concentration on somatic embryogenesis from cotyledonary explants of safflower was investigated. Embryogenic frequency as well as number of somatic embryos was dependent on auxin type and concentration. NAA at 10.74 μM (2 mg l−1) was optimum for high frequency of somatic embryos, whereas IAA provided the maximum number of somatic embryos per responding culture. Somatic embryo development was asynchronous and strongly affected by auxin type and concentration. Maximum numbers of well developed somatic embryos at the cotyledonary stage were obtained with 5.37 μM (1 mg l−1 ) NAA + 2.22 μM (0.5 mgl −1) BA. Histological studies confirmed the unicellular origin of somatic embryos from the adaxial epidermis of the cotyledon. Broad base attachment of somatic embryos to the epidermis indicated the absence of a suspensor.

Delineation of subsurface structures using self-potential, gravity, and resistivity surveys from South Purulia Shear Zone, India: Implication to uranium mineralization

The unexplored South Purulia Shear Zone (SPSZ) at the north of Singhbhum Shear Zone (SSZ) in Eastern India is a prospective zone for structural-guided hydrothermal mineralization. We carried out an integrated geophysical study using self-potential (SP), gradient-resistivity profiling (GRP), and gravity study across the SPSZ to identify the near-surface structural features and probable correlation with the uranium mineralization of the region. We studied a broad low SP, anomaly zone correlated with corresponding low-gravity and lowresistive zone across the same part of the study area. This conductive and low-density zone was identified as the width of the brittle-to-ductile and highly altered SPSZ. The 2D modeling of SP and residual gravity data along a northeast–southwest profile across the shear zone between Raghunathpur and Barabazar localities revealed the northerly dipping shear zone with an average width of ∼4.5 km. However, the 2D modeling of the SP data suggested numerous thick, sheet-type vertical and/or inclined structures intervening the shear zone, which were well correlated with the vertical structures delineated by the 2D gravity inverse model. The vertical alteration zones (density and conductivity) at ∼40-, 200-, and 400-m depths have been identified over this region. These alteration zones are likely to be mineralized zone because a hydrouranium anomaly has also been reported from those locations earlier. We studied the efficacy of an integrated approach using GRP, SP, and gravity surveys for the investigation of near-surface vertical to dipping conducting structures associated with uranium mineralization in such shear zone regions.

Geophysical anomalies associated with uranium mineralization from Beldih mine, South Purulia Shear Zone, India

Beldih mine at the central part of the South Purulia Shear Zone (SPSZ) has been reported with low grade uranium-bearing formation within quartz-magnetite-apatite host in kaolinized formation. Therefore, the present integrated geophysical study with gravity, magnetic, radiometric, very low frequency electromagnetic (VLF) and gradient resistivity profiling methods around the known mineralized zones aimed at identifying the exact geophysical signatures and lateral extent of these uranium mineralization bands. The closely spaced gravity-magnetic contours over the low to high anomaly transition zones of Bouguer, reduced-to-pole magnetic, and trend surface separated residual gravity-magnetic anomaly maps indicate the possibility of high altered zone(s) along NW-SE direction at the central part of the study area. High current density plots of VLF method and the low resistive zones in gradient resistivity study depict the coincidence with low gravity, moderately high magnetic and low resistivity anomalies at the same locations. Moderate high radioactive zones have also been observed over these locations. This also suggests the existence of radioactive mineralization over this region. Along profile P2, drilled borehole data revealed the presence of uranium mineralization at a depth of ∼100 m. The vertical projection of this mineralization band also identified as low gravity, low resistivity and high magnetic anomaly zone. Thus, the application of integrated geophysical techniques supported by geological information successfully recognized the nature of geophysical signatures associated with the uranium mineralization of this region. This enhances the scope of further integrated geophysical investigations in the unexplored regions of SPSZ.

Integrating Apparent Conductance in Resistivity Sounding to Constrain 2D Gravity Modeling for Subsurface Structure Associated with Uranium Mineralization across South Purulia Shear Zone, West Bengal, India

South Purulia Shear Zone (SPSZ) is an important area for the prospect of uranium mineralization and no detailed geophysical investigations have been carried out in this region. To delineate the subsurface structure in the present area, vertical electrical soundings using Schlumberger array and gravity survey were carried out along a profile perpendicular to the SPSZ. Apparent conductance in the subsurface revealed a possible connection from SPSZ to Raghunathpur. The gravity model reveals the presence of a northerly dipping low density zone (most likely the shear zone) extending up to Raghunathpur under a thin cover of granitic schist of Chotanagpur Granite Gneissic Complex (CGGC). The gravity model also depicts the depth of the zone of density low within this shear zone at ~400 m near Raghunathpur village and this zone truncates with a steep slope. Integration of resistivity and gravity study revealed two possible contact zones within this low density zone in the subsurface at depth of 40 m and 200 m. Our study reveals a good correlation with previous studies in Raghunathpur area characterized by medium to high hydro-uranium anomaly. Thus the conducting zone coinciding with the low gravity anomaly is inferred to be a possible uranium mineralized zone.

Enhancement of fault interpretation using multi-attribute analysis and artificial neural network (ANN) approach: a case study from Taranaki Basin, New Zealand

Enhanced seismic data conditioning and multi-attribute analysis through non-linear neural processing workflows has been applied to 3D seismic data over 215.10 km2 area of the Opunake prospect located in the south-eastern offshore Taranaki Basin. The present work aims to delineate faults and the related detail of structural features from the study area. Post-stack seismic data conditioning techniques such as dip-steering and structural filtering are applied to enhance the lateral continuity of seismic events and eliminate random noises from the data with the objective of improving the visibility of faults in the data volume. The conditioned data is then used to extract several attributes, such as similarity, dip variance, curvature, energy and frequency, that act as potential contributors for enhancing the fault visibility. A fully connected multilayer perceptron (MLP) network is developed to choose the proper combination of attributes for fault detection. These seismic attributes (known as the test datasets) are then trained at identified fault and non-fault locations using this network. The network comprises of 11, 7, and 2 nodes in the input layer, hidden layer and output layer, respectively. The neural training resulted in an overall minimum root mean square (RMS) misfit and misclassification (%) ranging from 0.54 to 0.67 and 18.67 to 10.42, respectively, between the trained and the test datasets. The neural training generates a fault probability attribute that produces an improved fault visibility capturing the minute details of the seismic volume as compared with the results of individual seismic attribute. Thus, the present work demonstrates an enhanced and robust workflow of fault prediction and visualisation for detail structural interpretation from 3D seismic data volume. This paper describes an improved and efficient workflow that refines the art of structural interpretation from 3D seismic data. The research aims to streamline the interpretation workflow using better data conditioning scheme and defining a meta-attribute (fault probability cube) using an artificial neural network. A robust pathway is provided for delineating structural details of complex geological terrain.

Laterite Covered Mafic-Ultramafic Rocks: Potential Target for Chromite Exploration - A Case Study from Southern Part of Tangarparha, Odisha

Exposed chromite deposits in the Sukinda belt, Odisha, India, have already been identified and exploited; but a large part of the area is covered by laterite and remains unexplored. As a case study to establish the feasibility of chromite exploration under laterite rocks, an integrated ground-based gravity, magnetic and very low frequency (VLF) - electromagnetic study was performed over a laterite-covered area at Tangarparha within the belt. North of the present laterite-covered area, a quartzofeldspathic gneiss contains proved chromite pods within ultramafic complexes. The gneiss-laterite contact is depicted by a transition from low to high in both gravity and magnetic anomaly maps at the northern part of the present study area. High Bouguer and residual anomalies (> 10 mGal and > 1 mGal, respectively) within the laterite-covered area indicates the existence of a high density rock in the sub-surface. The 2D models of the residual gravity anomaly depict the presence of high density (> 3570 kg/m3) layer under the laterite cover. The 2D magnetic models mostly reveal shallow surface effects of laterite covers. However, along profiles P2 and P3 high magnetic susceptibilities are detected at depths ≥ 20 m, and are likely to be caused by sub-surface chromite mineralization, as the locations are coincident with gravity highs. High current densities in VLF profiles are also recorded at the same locations confirming the presence of conducting sub-surface layer. Thus, the zone with high density, magnetic susceptibility and conductivity is most likely to be a chromitite-bearing sub-surface layer. The targeted chromite ore is distributed in east-west direction in the form of discontinuous pods of variable vertical thickness and strike lengths at the centraleastern part of profiles P2 and P3. The present study demonstrates that integrated use of ground gravity, magnetic and VLF techniques can effectively identify the target chromite deposits even under lateritic cover.

Improved Compact Inversion Approach For 2D Gravity Data Modelling Using Probabilistic Bounds

This paper is an improved version of the compact inversion approach. In the latest improvement by Ghalehnoee et al. (2017) depth weighing matrix and kernel weighing matrix were introduced to take care of the decay of kernel to depict the exact location, size and density of anomalous mass. Though it has improved the results but it could not reveal the exact shape and depth of the bodies and problem were also observed in the higher noise level. Therefore, in the present work a modified compact inversion approach is proposed by adding a probabilistic bound in the weighted least square solution in MATLAB. Application of this approach to the synthetic and field data sets depict the superiority in delineating the shape and depth of the causative sources compared to its predecessors.

Integrated gravity-magnetic study for delineation of structural guided uranium mineralization zones at Kutni, Purulia, West Bengal

The hydrothermally altered vein type uranium mineralization has been reported at different places along the South Purulia Shear Zone (SPSZ) towards 50 km north of the Singhbhum Shear Zone. An integrated close grid gravitymagnetic study over nearly one km2 area between Kutni and Dandudih villages within this shear zone has been performed to delineate the detail structural features, depth continuation, and associated uranium mineralization zones. The observed Bouguer and calculated residual gravity anomaly map depicts an ESE-WNW (on the east) to E-W (on west) trending low gravity zone on the extreme northern side of the area. The total field magnetic anomaly map also depicts the presence of high anomaly patches which is in accordance with the field observation of the exposed iron oxides (e.g. magnetite and goethite) over the same part of the study area. The 2D inverse modeling across the northern low residual gravity anomaly zones reveals steeply dipping low density structures with dip due north, south or vertical at places. The NS widths of these zones vary from 50-300 m with maximum probable depth extent of ~220 m. Previous researcher has also reported high radioactivity over the exposed quartz-magnetite-apatite bands on the northern part of the area. This band is exactly coinciding with the presently identified low gravity and high magnetic anomaly zones. These anomaly zones on the northern part of the study area are concluded to be hydrothermally altered uranium mineralization target zones. Thus, the results of this study will provide important guiding parameters for the future exploration programme over this region.