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GENESIS OF HIGH GRADE IRON ORE FROM BIF IN DALLI-RAJHARA, CHHATTISGARH, INDIA

Sun, 01 Oct 2017 00:00:00 GMT

Title: GENESIS OF HIGH GRADE IRON ORE FROM BIF IN DALLI-RAJHARA, CHHATTISGARH, INDIA Authors: Rastogi, Atul Kumar Abstract: Iron is one of the most important metal used in the world mainly for iron and steel industry to meet the requirement in infrastructural development. For the purpose it requires the high grade iron ore more suitably lumpy ore without any other deleterious elements like silica, alumina and phosphorous which is readily get attached to iron ore from its protolith in the nature. The iron ore occurs in varied geological environment such as sedimentary, hydrothermal and magmatic origin. However, World’s most high-grade iron ore deposits are associated with Banded Iron Formation (BIF). Unlike other protore rocks for metallic minerals deposits BIF itself consist of 30-35 wt percentage of iron (Klein 2005). BIF then upgraded to high grade iron ore (>64 wt. % Fe) through complex geological processes. This process of upgradation may take place geologically rapid < 5million years as established for many hydrothermal systems (Chiaradia et. al., 2014) or it may be as long as 100 million years. In case iron ore is further upgrade by weathering/supergene processes, which is mostly took in last 20 million years (Angerer et. at., 2014). India is also one of the leading producer of iron ore. Nearly all major deposits of high-grade iron of India occurs in association with BIF of all four major Cratonic areas. The Banded Iron Formation is popularly known as BHQ/BMQ/BHJ/ BMJ in India. The iron ore distribution in India has been classified in following five zones (designated as Zone-A to Zone- E) The study area for this work is Dalli-Rajhara, which lies in the zone-B. Several major iron mines occur in the Dalli –Rajhara Iron ore belt, which is the northern extension of Bailadila iron ore group of Bastar Craton in Chhattisgarh, where metamorphosed and heterogeneously deformed Banded Iron Formation (BIF) is regionally called Banded Hematite Quartzite (BHQ), was transformed into high-grade (Fe >64%) hematite ores. The area has been chosen because of the suitability of development of diverse kind of high-grade iron ore at one place and it also been academically less studied The objective of the present study mainly focus on the systematic change in mineralogy and geochemistry while enrichment from least BIF into high-grade iron ore. The characteristic and source of fluid responsible for this selective leaching. In addition, response of Au, Ag, PGEs during the process of high-grade iron ore formation. Based on hardness, two distinct type of high-grade iron ore are occurred in mines; hard and soft ore. Both the ore type having the laminated and massive textures. All the mine are mainly ii dominated by laminated ore from very hard to soft nature. Despite of various hardness and textural variation, mineralogically the ore are monomineralic i.e. hematite and martite (a low temperature pseudomorph of magnetite). Hematite grains are having several habits such as granular, tabular to anhedral. Gangue minerals are rarely present in hard ore, in soft are there may be presence of some Mn-oxide and ferrihydrites such as goethite and lepidorocite in micropores. Chemically high-grade iron ore either hard or soft entirely composed of Fe2O3 with a minimal presence of SiO2 but Al2O3 and phosphorous is seldom present in soft ore. Both the ore types are depleted in trace elements. The high-grade iron ore of Dalli-Rajhara show dual phenomenon of ore genesis; hypogene as well as supergene processes. The occurrence of hard massive iron ore within unaltered BHQ is the signature of hypogene process and presence of core stones (undigested BHQ) within soft ore marks the incomplete leaching of silica by meteoric water, as the silica is easily removed/leached in comparison to hematite. EPMA studies confirms the presence of precious metals such as Silver and Gold especially in pore spaces created while water circulation. These metals are present in BHQ as well as in ores; they are supposed to be more enriched in ores that are modified by supergene processes as they are resistant to chemical weathering. Trace elements concentration signifies that whole ore body is affected by supergene alteration. BHQ generally showing near to flat REE pattern having significant negative Eu anomaly but all the enriched iron ore showing some increase in LREE and positive Ce anomaly. There is two population of V concentration in massive as well as laminated ore signifies V concentration enriched in ores that are oxidized during meteoric alteration. Co and Cu remain in positive correlation with the Fe2O3. The fluid inclusion studies were carried out in some of the selected quartz vein samples collected from the ore zone. These veins are supposed to be precipitated during the mineralization/ enrichment. Based on petrography primary secondary and some of the pseudo-secondary inclusions are identified. Most of these inclusions are biphase aquous (Type I) another is liquid rich carbonic biphase inclusion (Type II). Only primary inclusion are taken into consideration in this study. The homogenization temperature of Type I inclusion is varies between 122-344˚C and salinity of Type I varies from 0.18- 35.41 wt. % NaCl equiv. XPS analysis of samples give some exciting result as it give good concentration of PGEs in BHQ and getting enriched in iron ores. The main PGE that is consistently present are Ru, Os iii and Pt. The presence of PGE in this deposit is being reported here at the first time. This requires an extensive study for scientific and economic purpose to be use the deposit for the future resource for the extraction of the PGE especially Platinum and Osmium. The iron ore deposits of the study area may also be defined as supergene modified hydrothermal iron ore deposit. The mineralization is normally found northern flank of the hills and the area has undergone atleast two phases of deformation, which created numerous easy passage for the circulation of meteoric water, causing an effective leaching of silica. Thus, a structural/ physiographic control is there for the localization of ore. Apart from the high-grade iron ore, the study area can be good a prospect for the economic resource of PGE in future.

3D MAGNETOTELLURIC AND DCR INVESTIGATIONS AT SELECTED SITES IN UTTARAKHAND

Fri, 01 Nov 2019 00:00:00 GMT

Title: 3D MAGNETOTELLURIC AND DCR INVESTIGATIONS AT SELECTED SITES IN UTTARAKHAND Authors: Devi, Anita Abstract: Electrical resistivity structures at four selected regions were deciphered from 3D inversion of Magnetotelluric (MT), Radio Magnetotelluric (RMT) and Direct Current Resistivity (DCR) data recorded in Uttarakhand, India. Earlier, the recorded MT and DCR data from the regions were interpreted assuming a 2D model of Earth. However, the geological structures, in general, are 3D in nature. Hence, the MT, RMT and DCR data, recorded by our group prior to the onset of this study along with the data recorded during the present work, are analyzed using 3D inversion techniques. The entire data comprises four different case studies, (i) MT data recorded in the Garhwal Himalayan Corridor (GHC) along Roorkee-Gangotri (RG) profile, (ii) MT data recorded in and around MCT zone in Chamoli region, (iii) DCR data recorded near a proposed bridge site in Tehri region and (iv) DCR and RMT data recorded in Saliyar Village near Roorkee. The first case study is an MT investigation in GHC where MT data were acquired at 39 sites on RG profile. AP3DMT, a MATLAB based code developed by our group, was used for 3D inversion of this MT dataset. Before performing this 3D inversion several 3D synthetic inversion experiments, on full impedance tensor data, were carried out to estimate the optimal values of important control parameters affecting the inversion results. The synthetic studies established that the off-profile resistivity structures within 20 km from the profile can be deciphered from profile data. The optimal values of some other inversion parameters (e.g. model grids, smoothing, regularization parameter etc.) were also inferred and then used for 3D inversion of the field data. A 3D geoelectric model was obtained after performing several 3D inversion experiments on RG profile MT data using different components of data independently and jointly. The data types used were vertical magnetic field transfer function (VTF), Phase Tensor (PT), full impedance tensor (Z), VTF + PT and VTF + Z. Based on sensitivities of Z and VTF data and on other related tests, the model obtained from the VTF + Z data was chosen as the final model for detailed interpretation. The robustness of important features in the inverted model were validated through sensitivity tests. The model defines the geometry of DHR beneath the IGP, SH and LH in Garhwal Himalayan region. The model also suggests that DHR is a fault bounded structure. The obtained 3D geoelectrical model reveals some new off-profile resistivity structures which are aligned transverse to the main iii Himalayan arc. The off-profile structures are interpreted as conductive (< 10 Wm) fluid saturated fractured zones bounding the highly resistive (> 1000 Wm) Delhi-Haridwar Ridge (DHR). The 3D resistivity model explains the thrust tectonics and flat ramp flat geometry of Main Himalayan Thrust (MHT). The model was also correlated with other geophysical models and with seismicity of the region. It has been observed that the earthquakes are generally located in the resistive zone of the crust with a few exceptions where they are near or in the conductive zone. In second case study, MT data recorded at 28 sites in and around MCT zone in Chamoli region of Uttarakhand, India were inverted using the code AP3DMT. The dimensionality and directionality analysis of the MT data revealed the dominant 3D nature of the impedance tensor. In first step, the dataset was inverted for 28 sites. However, due to some noisy sites data, 23 MT sites were selected for obtaining the final 3D model. The 23 sites were inverted using the full impedance tensor data. Experiments were done to test the consistency, robustness and stability of the obtained 3D geolectrical model. Experiments were also done to identify the depth of investigation upto which the model is valid. The main highlight of the resistivity model is the presence of two doublets comprising low-high resistivity features. One of the doublet (‘AB’) is located in MCT zone and Inner Lesser Himalaya and the second one (‘CD’) in Higher Himalayan region. The low resistivity feature of the doublet represents the fluid saturated fracture zone while the high resistivity feature represents the brittle rigid rocks. The conductive features (‘A’ and ‘C’) are related to the change in porosity, fluid content, pore distribution and possibly high heat flow and these can be explained in terms of the fluid saturated sediments adjacent to the resistive rigid rock matrix (‘B’ and ‘D’). The resistivity model supports the role of fluid in triggering the medium and large size earthquakes in the region. The model features were correlated with the velocity model obtained from seismic tomography studies. The resistivity model also explains the high heat flow and the presence of thermal springs in the area. The third case study was a ERT study where the data were used to characterize the subsurface soil at a bridge foundation site on the banks of Bhagirathi River at Tehri reservoir site, Uttarakhand, India. For this, six Electrical Resistivity Tomography (ERT) profiles were recorded on West and East banks of the river and these profiles were interpreted to determine the electrical resistivity image of the subsurface. The 2D and 3D subsurface resistivity models were obtained after inverting the data using the inversion codes Res2dinv iv and AP3DMT-DC respectively. Based on the 2D and 3D ERT inversions, the resistivity of different lithological units have been defined for the investigated sites. The basement depth has been found on the basis of resistivity variation. The basement depth was found on the basis of resistivity variations. The borehole data and geological inputs were used for lithological correlation and calibration of the resistivity values to the subsurface formation. The Standard Penetration Test (SPT) data (N-values) were correlated with the extracted resistivity values at selected points of the inverted models. The correlation study shows that resistivity is linearly correlated with the N-values. The coefficient of correlation was greater than 0.85, indicating that it is good and consistent. The relationship is site specific but useful for geotechnical investigations in the Himalayan region where undertaking a destructive test is prohibited. The last case study deals with the ERT and RMT data from Roorkee region which were used to study the effect of groundwater contamination due to untreated sewage irrigation near the Saliyar village, Roorkee. Nine RMT and five ERT profiles were recorded in and around the contaminated zone and one ERT and one RMT profile were recorded in the uncontaminated zone, for comparison. The two datasets were inverted independently as well as jointly using the 3D inversion code AP3DMT-DC. Prior to this, a synthetic study was carried out to validate the algorithm capabilities. This study demonstrated that the two methods, ERT and RMT, complement each other and that in the inverted model obtained through joint 3D inversion the resistivity values and geometry of the low and high resistivity features are better resolved than the models obtained through individual inversions. In the present study, the 3D models obtained after inversions of field data were found to be consistent with the published results of 2D inversion. The 3D inverted resistivity model shows an unconfined aquifer of low resistivity which is overlain by a slightly resistive near surface unsaturated soil formation. Moving away from the waste disposal site, an increase in resistivity was observed for the shallow unconfined aquifer. In comparison to the inverted results of an uncontaminated reference site, the inverted results of the contaminated region show a decrease in resistivity of the aquifer layer establishing the influence of contamination. The results of 3D joint inversion of the two datasets were encouraging in terms of accuracy and resolution of the model features and better explains the resistivity variation and geometry of all the features than the models obtained by individual inversions.

PALEOGEOGRAPHIC AND PALEOCLIMATIC RECONSTRUCTION ALONG THE MAHANADI DELTA

Mon, 01 Jul 2019 00:00:00 GMT

Title: PALEOGEOGRAPHIC AND PALEOCLIMATIC RECONSTRUCTION ALONG THE MAHANADI DELTA Authors: Dash, Chinmay Abstract: The present study on Mahanadi delta has two broad objectives: (i) to define implications of sea-level fluctuations on channel morphologic changes in deltaic environment and, (ii) to reconstruct Indian Summer Monsoon variability from lake sediment records. Contrary to previous laboratory-based investigations lacking empirical evidence on fluvial response to base-level changes, the present work is focused on correlating concepts of base-level controlled channel morphologic changes with fieldbased observations. Various paleo-fluviogeomorphic features such as anastomosingmeandering transition, paleo-dendritic channels, and lateral shift of river mouths, which are indicative of base-level change have been studied and correlated with past marine transgression and regression events. Past studies on borehole cuttings indicate that the Mahanadi delta has experienced several episodes of marine transgression and regression events. Paleo-barrier spits, relict ridges, and paleo-marine terraces in the inner Mahanadi deltaic region are evidence of past coastline positions. Ground Penetrating Radar study along paleo-strandlines of the Mahanadi delta reveals several stratal termination units in the sub-surface sediment layers. These subsurface depositional units may have developed due to repeated marine transgression/regression and sequential deposition of sediments. Major rivers in the Mahanadi delta e.g. Mahanadi, Devi, Brahmani, and Baitarani, show episodic anastomosing and meandering characteristics corresponding to transgressive and regressive events, respectively. The paleo-anastomosing branches along the paleo-strandline positions can be observed in satellite imagery. Dendritic drainage patterns formed due to flow accumulation along the coast have been observed along the paleo-strandlines. Based on OSL ages and affinity to strandline positions, two generations of Holocene dendritic channels can be distinguished in the Mahanadi deltaic region. Paleo-dendritic channels with age > 5 ka BP correspond to Early-Mid Holocene strandline position and, with age group < 5 ka BP correspond to the Late Holocene strandline position. The Early to Mid and Mid to Late Holocene paleo-dendritic channels developed along the transgressive coasts and later were abandoned when the coastline regressed. Lateral shifting of river mouths in response to sea-level changes have been observed in the lower deltaic plain. The delta distributaries such as Bhargavi, Kushavadra, Brahmani and Baitarani rivers ii show lateral shift of river mouth before meeting the Bay of Bengal. Age of Kushabhadra River paleochannel indicating paleo-flow direction dates back to ~ 7 ka BP. Similarly, the paleo-flow paths of the Brahmani River date back to ~ 6 ka BP. The river mouth shift directions of both the rivers are parallel to the Early Holocene strandline. Major rivers in the delta have migrated up to the present coastline with base-level adjustments to changing coastline, while the small channels ended abruptly with a retreat in sea level. Paleochannels along the paleo-strandlines indicate last fluvial activity along the paleo-coastlines. When compared to fluvial morphological patterns along paleostrandlines of major deltas around the world, the Mahanadi delta shows similar paleofluvial morphology with changing coastline. Two sediment cores from Anshupa Lake and Chilka Lake were analyzed to study paleoclimatic changes and their effect on sedimentation in the Mahanadi delta region. Sediment core from Anshupa Lake dates back (14C) to 1400 AD, provides evidence of the Little Ice Age (LIA). The average sedimentation rate during LIA was 0.12 cm/yr and it drastically changed to 0.45 cm/yr in the post LIA period. During the LIA period, the sedimentation rate was highest in the 16th century (0.35 cm/yr) and lowest in the 18th century (0.09 cm/yr). Down core variation of mineral magnetic, organic carbon and stable isotope record suggest that LIA extended from 1450 AD to 1850 AD. The 𝜒𝑙𝑓 values vary from ~ 5× 10− 8 m3 kg− 1 to ~ 60× 10− 8 m3 kg− 1. The 𝜒𝑙𝑓 values are lower at the Dalton (~ 5× 10− 8 m3 kg− 1) and Munder Minimums (~ 9× 10− 8 m3 kg− 1), while the 16th century showed an increasing trend. The χfd % value varies from ~0 to ~13%. The χARM value varies from 0.785 × 10− 5 m3 kg− 1 to 0.021 × 10− 5 m3 kg− 1. The saturation isothermal remnant magnetization value varies from 627.0126× 10− 5 Am2 kg− 1 to 33.094× 10− 5 Am2 kg− 1. χfd %, χARM and SIRM show similar trend as shown by 𝜒𝑙𝑓 values. The 𝜒𝑙𝑓 shows a positive correlation with reconstructed sunspot numbers. Spectral analysis of χlf values shows significant periodicity of 74, 64, 44 and 11 years. These periodicities suggest a solar influence on Indian Summer Monsoon. Organic carbon and nitrogen percentage vary from 1.5 to 6 % and 0.07 to 0.7 %, respectively. The δ13C value of organic carbon fluctuates from – 21.028 to − 26.528 ‰. The downcore variation of δ13C and TOC reflects two phases of climate during LIA. Phase-I (1450 to 1700 AD) reflects relatively high content of TOC and more negative values δ13C indicating relatively warmer climatic condition. During Phase-II (1700-1850 AD), TOC deposition relatively decreased and δ13C iii became comparatively positive reflecting relatively cold climate. The inter-parametric ratio χARM/SIRM is > 200 around 1600 AD, suggesting the presence of bacterial magnetism. Bacterial magnetite develops due to a high influx of nutrients into the lake. The bacterial magnetism correlates with high nutrient supply to the lake ecosystem due to a relatively warm period during the 16th century, as suggested by an increasing trend in 𝜒𝑙𝑓 values. The organic carbon percentage, C/N ratio and stable isotope record indicate comparatively increased rainfall during the 16th century than the 17th and 18th centuries. From these geochemical parameters, it is inferred that the 17-18th century corresponding to Dalton Minimum was the coldest period with reduced precipitation and the 16th century was a relatively warmer period during LIA. Several events of drought, high rainfall, and the onset of aridity can be correlated with similar events documented in speleothems from different parts of India. The sediment core from Chilka Lake dates back to 9039 cal yr. BP. Sedimentation rate fluctuates from ~ 0.2 cm/year to ~ 0.007 cm/year, with maximum sedimentation from 8,000 cal yr BP to 6,000 cal yr BP and minimum sedimentation from 6,000 cal yr BP to 2,000 cal yr BP. Down core variation of mineral magnetic parameters reveals wide fluctuation in 𝜒𝑙𝑓 values. The 𝜒𝑙𝑓 values range from 6.4× 10− 8 m3 kg− 1 to 43× 10− 8 m3 kg− 1. The 𝜒𝑙𝑓 values are minimum from 6,000 cal yr BP to 2,000 cal yr BP, suggesting mid-Holocene weakening of Indian Summer Monsoon. χARM varies from 0.71 × 10− 5 m3 kg− 1 to 0.021 × 10− 5 m3 kg− 1. The saturation isothermal remnant magnetization values vary from 636.33× 10− 5 Am2 kg− 1 to 44.905× 10− 5 Am2 kg− 1. The downcore variation of 𝜒𝑙𝑓, χARM, and SIRM show a similar trend. An increasing trend in these mineral magnetic parameters are observed during early to mid (8,000 cal yr BP to 6,000 cal yr BP) and late Holocene period (>2,000 cal yr BP). The study of Chilka Lake core suggests Holocene warm period extended from 9,000 cal yr BP to 6,000 cal yr BP, and the mid-Holocene period was relatively cold. Regional records on flourishing and extinction of river valley civilizations are found to be correlated with climatic records obtained from Chilka Lake core. Spectral analysis of 𝜒𝑙𝑓 values shows significant periodicities of 1058, 690, 484, 396, 288, 212, 207, 183 and 158 years, suggesting a possible solar influence on Holocene variation of Indian Summer Monsoon. Paleoclimatic study from two sediment cores suggests that magnetic susceptibility (χlf) data is highly correlating with regional climatic records. Spectral analysis of χlf in both the cores indicates that periodicities in ISM can be obtained from high-resolution magnetic susceptibility data. We have thus explored the potential of using magnetic susceptibility (χlf) as a proxy for paleorainfall variations in a tropical region.

LANDSLIDE HAZARD EVALUATION OF HILL SLOPES IN AND AROUND MUSSOORIE TOWNSHIP, INDIA

Mon, 01 Jul 2019 00:00:00 GMT

Title: LANDSLIDE HAZARD EVALUATION OF HILL SLOPES IN AND AROUND MUSSOORIE TOWNSHIP, INDIA Authors: Preethambaran, Bipin Abstract: Landslides are a widespread and frequently occurring natural hazard, which cause serious damages to lives and property, especially on mountainous terrains (Anbalagan et al., 2008). Particularly, landslide occurrences are more important in highly urbanized hill stations where they may cause severe damages to properties and affect human life (Anbalagan et al., 2008). India’s long Himalayan Mountain in the north is geologically a young range of mountain chain. Every year this region faces several hundreds of landslides, from Jammu & Kashmir to North Eastern states including Himachal Pradesh, Uttarakhand, and Sikkim Himalaya, leading to enormous loss of life and property (Anbalagan et al., 2007; Kumar et al., 2017). The Uttarakhand Himalaya has been a hotspot for landslide related researches, particularly in the last two decades due to the frequent occurrence of landslides and increased pressure of urbanisation in the region (Gupta et al., 2013, 2000, 1993; Gupta and Anbalagan, 1997; Kumar et al., 2008 Ray et al., 2009) In this context, stability of hill slopes in and around heavily urbanized township of Mussoorie have been evaluated systematically in order to identify suitable remedial measures and to identify suitable sites for future urbanization in and around the township.