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Slope failures along the road sections cause huge problems every year in Sikkim. A slope instability analyses was performed along the road sections in parts of West Sikkim. The study was supported by geotechnical analyses like rock mass rating (RMR) and slope mass rating (SMR). In order to identify different failure types stereographic plotting based kinematic analyses was performed. Out of 33 study sites for the geotechnical analyses, 24 sites were identified as wedge failure and the remaining 9 sites were identified as the planar failure. Highly metamorphosed rocks like quartzite, phyllite and gneiss were the common rocks found in the area, comprising the discontinuities like joints were found up to 4 sets in certain locations. Other tectonic discontinuities include main central thrust (MCT), Tista lineament and other inferred thrust. Several such structural discontinuities and the weak lithology have made the area extremely vulnerable. The RMRbasic values varies from 26–60 in the study area which falls in the good to average category rocks. Adjustment factors were added to the RMRbasic to calculate the SMR values, which ranges between 26–74 and falls in good to bad rock mass description. Based on the different values for the SMR ratings, supportive measures were recommended for the different study locations. These are spot or systematic bolting, spot shotcrete, systematic anchors, systematic shotcrete, toe wall, dental concrete, systematic reinforced shotcrete, re-excavation, deep drainage, etc. and bioengineering treatment. [ABSTRACT FROM AUTHOR]

The present investigation reveals that the Basal Conglomerate is ∼ 2–3 m thick forming basal part of the Vindhyan Supergroup in the Sonbhadra district, central India. The Basal Conglomerate consists of fragments of different rock types supported by the sandy matrix. It contains pebble-sized clasts of quartzite, jasper, phyllite and slate dominated by the quartzite clasts. The matrix is composed of sandy material that is rich in quartz, chert and iron oxides. The occurrence of quartzite clasts suggests its derivation from the Chhotanagpur Granite Gneiss Complex (CGGC) and the phyllite, slate and jasper suggest their derivation from the Mahakoshal Group. The presence of polycrystalline and monocrystalline quartz suggests their derivation from Chhotanagpur Granite Gneiss Complex and the presence of chert suggests its derivation from the Mahakoshal Group. The iron oxides were produced as a result of leaching of iron during chemical weathering. The X-ray diffractometry of the matrix suggest ubiquitous presence of quarz, muscovite and kaolinite. The kaolinite has formed due to alteration of feldspars under warm and humid conditions. This is also supported by the presence of ferruginous matter in the matrix. [ABSTRACT FROM AUTHOR]

The status of the Proterozoic volcano-sedimentary Simlipal complex (covering latitudes 21°14′–22°20′N and longitudes 86°03′–86°35′E) of Singhbhum, eastern India remains unclear till date. The Simlipal complex has classically been designated to represent three layers of alternate spilitic volcanics and quartzite deposited in a geosyncline that unconformably overlies the meta-sedimentary Singhbhum Group of rocks. The study of the authors (entailing digital elevation map) bring out that the concentric ring-like outcrop pattern of Simlipal complex is only topography-controlled and repetitive bands of quartzite and volcanics do not exist. Further, it has been documented that the Simlipal complex comprises basemental weakly metamorphosed quartzite-phyllite (∼450m thick) heterolith unit (proposed Lulung Formation), which is followed upward by fresh, sub-horizontal (∼250m thick) volcanic unit (proposed Barehipani Formation) with local presence of peridotite-gabbro, and finally to quartz arenite unit (∼150m thick) as the topmost layer (proposed Jurunda Formation). The heterolith unit (proposed Lulung Formation) has been envisaged as a part of the older Singhbhum Group. The basaltic rocks (Barehipani Formation) correspond to calc-alkaline tectonic affinity based on geochemistry. We propose an arc-subduction related setting for the Simlipal complex which may be further confirmed through detailed major/trace elements and isotopic studies. [ABSTRACT FROM AUTHOR]

Singhbhum craton preserves the records of sedimentation, magmatism, and tectono-thermal events from Mesoarchaean to Neoproterozoic. The Dhanjori Group (DG), located on the northeast margin of the Singhbhum craton, comprises of a variety of rocks including quartz pebble conglomerate, quartzite, schist, inter-layered with mafic to intermediate and rarely acidic lava flows, tuff and agglomerate. Petrography and geochemical characteristics of the Dhanjori quartzite have been undertaken to interpret paleoweathering and provenance characteristics. Studied quartzites are made up of abundant quartz, feldspar, mica, and lithic fragments. With the help of geochemical data, the studied quartzites are classified as quartz-arenites and sub-arkoses. In addition to the A-CN-K plot, various chemical indices such as the chemical index of weathering (CIW), chemical index of alteration (CIA), and plagioclase index of alteration (PIA) indicate moderate to intense chemical weathering of the provenance under semi-humid climatic conditions. Rare earth element (REE) chondrite normalized patterns of the studied samples illustrate enriched light rare earth elements (LREEs) (LaN/SmN = 3.11–6.19), depleted heavy rare earth elements (HREEs) (GdN/YbN = 0.35–3.12) and negative Eu anomaly (Eu/Eu* = 0.55–0.87, ∼ 0.68). Such patterns are similar to that of the upper continental crust (UCC). In the discrimination function diagram, studied samples of the Dhanjori Group fall in quartzose sedimentary field. In addition, La/Sc vs. Th/Co and La-Th-Sc diagrams, various ratios like Th/Sc (∼0.61), La/Sc (∼4.42), Th/Co (∼0.03), La/Co (∼0.11), and Cr/Th (∼141.62) imply a mixed provenance for the studied samples. Hence, it has been inferred that the meta-sediments and ortho-amphibolites of the older metamorphic group, Singhbhum granitoid complex, as well as associated Archaean metavolcanic suites, would have acted as the probable source rocks for the studied Dhanjori quartzites. [ABSTRACT FROM AUTHOR]

Paleo-Mesoproterozoic (1.0-2.4 Ga) north Singhbhum mobile belt (NSMB) is one of the prominent polymetallic mineral belt within the Singhbhum crustal province of eastern India lying between Chotanagpur gneissic complex (CGC) in the north and the Archaean Singhbhum craton (>2.4 Ga) in the south. The study area is located along the northern fringe of Dalma volcano-sedimentary basin. Lithological variations, structure, metamorphism and tectonic setting indicate good prospect for regional gold exploration within this area.Extensive work by Geological Survey of India (GSI) within this basin reveals gold occurrences with its concentrations ranging from 0.1 to 4 ppm within the carbonaceous cherty quartzite. Gold mineralization within the area has been reported to be associated with quartz ± quartz carbonate vein either as disseminated gold or as refractory gold within the sulfides. A detailed study on the occurrence of refractory gold associated with carbonaceous cherty quartzite has not been carried out by any of the previous workers. The present work report the occurrence of refractory gold associated with sulfides within the carbonaceous host rocks. Detailed petrographic studies of the carbonaceous host rock reveal the presence of sulfides such as pyrrhotite, pyrite, chalcopyrite, arsenopyrite. EPMA studies of the host rocks indicate the presence of invisible gold within the sulfides varying in concentration from 100 to 1000 ppm. Total organic carbon (TOC), high resolution X-ray diffraction (HR-XRD) and Fourier transform infrared spectrometry (FTIR) analysis show the presence of organic carbon within the samples. Presence of organic carbon facilitates reducing environment required for gold mineralization within carbonaceous host rock in the study area. [ABSTRACT FROM AUTHOR]

Quick depletion rate of high-grade iron ore paved to emphasise on banded hematite jasper and banded hematite quartzite with ~30-40% iron. In the present investigation, efforts have been made to characterize the banded hematite jasper of Ghatkuri area (Gua), west Singhbhum, Jharkhand, India. The banded hematite jasper of the study area have complex physical and mineralogical character. X-ray diffraction analysis indicated that silica and iron are the major phases whereas alumina and goethite are the gangue mineral. Thermo-gravimetric analysis revealed it to be oxy-hydrated with iron in hematite phase. Vickers hardness test and bond work index revealed hard and compact nature of the ore. Grain size analysis shows the maximum concentration of the elements at the size range of -125+106 μm whereas minimum at -212+180 μm. [ABSTRACT FROM AUTHOR]

Sedimentary structures are very useful in paleocurrent analysis and interpretation of siliciclastic shallow marine environment. These interesting sedimentary structures such as parallel bedding, cross bedding, ripples, and mud cracks as well as synaeresis cracks, are best studied in the field. They are formed by a variety of sedimentary processes, including fluid flow, sediment-gravity flow, soft-sediment deformation and biogenic activity. Gulcheru Formation has evidence of interaction of microbial communities with clastic sedimentation during Palaeoproterozoic time. Because of high porosity-permeability of siliciclastics of Gulcheru Formation, palaeontologists do not expect many fossils preserved in such rocks and thus they have been overlooked. Microbially induced sedimentary structures (MISS) are highlighted in the Gulcheru Formation. They are indicative of shallow marine environment. Gulcheru Formation shows alluvial fan to shallow marine shelf environments within a limited thickness of about ~ 110m, which indicates an alluvial plain coast where alluvial deposits are modified by wave forces. [ABSTRACT FROM AUTHOR]

The present paper demonstrates the assessment of slope stability analysis between Rampur to Jhakri road section along National Highway (NH-22), Himachal Pradesh, India. The different types of slope failures have affected most part of slopes which causes considerable loss of life and property, inconveniences such as disruption of traffic along highways. The poorly designed rock slopes for road widening or construction purposes may weaken the stability of the slopes. A detail field investigation has been carried out to collect the representative rock samples for determination of physico-mechanical properties of rock and joint data for kinematic analysis. The rocks exposed in the area are highly jointed quartzite and quartz-mica schist of Rampur-Larji Group of Palaeoproterozoic age. The continuous slope mass rating (CSMR) technique has been applied for the assessment of slope stability analysis at five vulnerable locations and the results shows slopes are partially stable to unstable. Kinematic analysis mainly shows wedge type of failure along with few toppling and planar failures. The existing slope required immediate treatment to prevent the failure for its long term stability. [ABSTRACT FROM AUTHOR]

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/m) 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. [ABSTRACT FROM AUTHOR]

Electron Backscatter Diffraction (EBSD) data of quartz are presented from two quartzite samples of the Lunavada Group (Aravalli Mountain Belt, India). The two samples lie at a distance of 4 km and 30 km from the eastern margin of Godhra granite, which is known to have emplaced syntectonically with late deformation of the Lunavada Group rocks. The sample located away from the granite has weak CPO and fine grain size. Quartz grains in the sample close to the granite are coarse and show strong CPO. It is concluded that heat supplied by the Godhra granite resulted in coarsening of grain size, and dislocation creep was an important deformation mechanism in the sample proximal to the granite. Weak CPO in sample away from granite maybe due to grain boundary sliding, which may have been favoured by the finer grain size of quartz in the sample. [ABSTRACT FROM AUTHOR]

The Mesoarchaean Iron Ore Group (IOG) of rocks in Bonai-Keonjhar belt is disposed in a horseshoe shaped synclinorium structure in the western part of the Singhbhum Craton. Morphology of this synclinorium is expressed by a near continuous western ridge and dissected eastern highlands with the broad Jamda-Koira valley at the centre. Detailed structural analysis in the northern part of the belt suggests that the synclinorium is in fact a series of NE-SW to NNESSW trending shallow plunging, second generation (D) syncline and anticline which have overturned, inclined, relatively tight geometry in the western part and upright, open to gentle in the eastern part. This structure is clearly manifested by synclinal ridges and anticlinal valleys. Evidence of an early deformational event (D) manifested by the presence of isoclinal folds on outcrop scale has been recorded. D and D are near co-axial. The last deformational event (D) has led to dome and basin interference pattern due to cross folding along NW-SE striking axial planes. The volcano-sedimentary package in the belt commenced with platformal package represented by basic volcanic-quartzite association. The Bonai range volcanic, Nuakot volcanic and the Jagannathpur volcanic occurring in the western, southern and eastern parts of the belt has been interpreted to be correlatable representing the basal volcanic suite. The linear body of basic volcanic occurring at the central part of the belt is found to be occupying the core part of a shallow plunging anticlinal axial trace and thus has also been equated with the basal volcanic suite. There is but only one major BIF horizon in the Bonai- Keonjhar belt which has been structurally repeated across the belt, BIF occurring as NNE-SSW trending synclinal ridges flanked on either side by the older phyllitic sequences. [ABSTRACT FROM AUTHOR]

From the recent research by several workers it is becoming evident that the geology, particularly the structure and metamorphism of the Proterozoic sedimentary basins are not simple, which can at times be compared with foldthrust belts. In the southern part of the Pranhita-Godavari (PG) basin in its close proximity with the Eastern Ghat Mobile belt (EGMB) in the east and Eastern Dharwar craton (EDC) in the west there is a supracrustal association exposed near Kothagudem in Andhra Pradesh, which was earlier referred in published literature as Mulug and Mallampalle Groups of lower Pakhal sequence. From the field and petrological studies we have attempted to enumerate here the deformation and metamorphic characteristics and the tectonic setup of this schistose unit. It is revealed from our studies that this lithotectonic unit represents a strongly deformed and metamorphosed deeper crustal supracrustal assemblage, which is in sharp contrast with the unmetamorphosed and weakly deformed true Pakhal sequence occurring in the western part of the area. In order to explain the spatial association of these two contrasting litho-tectonostratigraphic units we propose a westerly verging thrust model, supported by convincing structural and metamorphic evidences, whereby the schistose terrane is tectonically juxtaposed with the unmetamorphosed Pakhal sequence. Imprints of polyphase deformation and metamorphism could be recognized to document the complex history of the schistose terrane. At least three generation structures (D, D, D) are identifiable in quartzite-metapelite-carbonate assemblages. D and D are quite pronounced and conspicuous by the development of respective planar and linear elements, while D is relatively mild in intensity. Development of different generations of folds (F, F, F) and associated axial planar cleavage/ schistosity (S, S, S) together with different types of fold interference patterns, demonstrated mainly in carbonate rocks, bear testimony to successive events of fold formation as a result of superposed deformations. The tectonic trend defined by N-S to NNESSW (approx.) elongation of the belt results from the combined effects of all the three deformations. The structural pattern indicate a possible combination of predominantly pure shear and subordinate simple shear transpressional type of tectonism accompanied by considerable E-W (approx.) tectonic shortening across the belt. The rocks show low to medium grade metamorphism with the characteric appearances of chlorite, biotite, andalusite, chloritoid, staurolite and garnet porphyroblasts in pelitic rocks. From a study on 'S-S' tectonites in different mineral assemblages we have elucidated the history of deformation and metamorphic mineral growth in this assemblage. A variety of relationship exists between 'S' and 'S' demonstrating multi-stage growth of porphyroblasts, particularly of andalusite and staurolite, which took place during at least two deformational events. The important mineral assemblages include: (i) garnetbearing andalusite- biotite schist, (ii) garnet free andalusite-biotite schist, (iii) staurolite-andalusite-garnet-mica schist, (iv) andalusite-chloritoid-muscovite schist, and (v) garnet-chloritoid-chlorite-muscovite schist. The study establishes a prograde metamorphic evolution in each rock type followed by a retrograde history. But the relative timing of prograde and retrograde reactions with respect to successive phases of deformation varies widely. [ABSTRACT FROM AUTHOR]

Lattice Preferred Orientation (LPO) of quartz and muscovite are measured in a micaceous quartzite using SEM based Electron Backscatter Diffraction (EBSD) analysis. The measurements were done in a thin section prepared parallel to the KK plane of the anisotropy of magnetic susceptibility (AMS) ellipsoid, which is equivalent to the XZ plane of the strain ellipsoid. Bulk data from the sample reveal that quartz c-axis develop an oblique single girdle LPO pattern indicating a dextral sense of shear. A similar pattern is produced by poles to the basal planes (001) of muscovite, which implies that muscovite controls the LPO of quartz in the rock. Petrofabric analysis of quartz is performed in domains viz. (I) not containing muscovite, (II) between two muscovite grains, and (III) rim of quartz grains around a muscovite grain. Quartz LPO pattern in Domain-III is noted to be similar to the bulk LPO recorded from the whole sample, thus confirming that muscovite was critical in textural evolution of the rock. The study thus establishes that a minor mineral phase in a rock can control the LPO of the major mineral phase, thus playing a significant role in development of bulk texture of the rock. The advantages of domainal petrofabric analysis in evaluation of slip systems in minerals in different parts of a rock, and vorticity quantification are discussed. [ABSTRACT FROM AUTHOR]

Zoned Apatite crystals with intrinsic radioactivity are widespread in the S-type basement granite around Govardhanagiri-Chinnakolumulapalli-L.Banda areas of Kurnool District, A.P. The granite is overlain by Gulcheru quartzite and in turn by Vempalle dolostone of Papaghni Group belonging to the Cuddapah Supergroup. The area (4 km x 6 km) is characterized by conjugate fracture system comprising ENE-WSW and WNW-ESE of varying extents, of which, ENE-WSW is sympathetic to the major deep seated Gani Kalva fault. The apatite crystals are frequently zoned and vary in size from few microns to 1000 microns, occur mostly as veins or associated with pulverized matrix of granite cataclasite. Veins (upto 2 cm. thick) generally follow the major fracture-trend (ENE-WSW) in the area. The apatites are also found intimately associated with fluorite, tourmaline and sulphides, which suggest their derivation from pneumatolytic fluids. The intrinsic accessory uranium as scarce grains of uraninite and other labile phases of granite were remobilized consequent upon the deformation and locked up as ferroan-oxy/hydroxyl inclusions in slowly growing apatite crystals under very low temperature conditions. [ABSTRACT FROM AUTHOR]

Quartzitic pelites forms a part of Higher Himalayan Crystalline of higher geotectonic zone in Garhwal Himalaya. Quartzitic pelites (locally known as Pandukeshwar Quartzite) in Garhwal Himalaya is sandwiched between high grade metamorphic rocks of Central Crystallines and Badrinath Formation. Fluid inclusion studies are carried out on the detrital, and recrystallized quartz grains of quartzitic pelites to know about the fluid phases present during recrystallization processes at the time of maximum depth of burial. The quartzitic pelite (Pandukeshwar Quartzite) essentially consists of recrystallised quartz with accessory minerals like mica and feldspar. Fluid microthermometry study reveals the presence of three types of fluids: (i) high-salinity brine, (ii) CO 2-H 2O and (iii) H 2O-NaCl. These fluids were trapped during the development of grain and recrystallization processes. The high saline brine inclusions and CO 2-H 2O fluid with the density of 0.90 to 0.97 gm/cm 3 are remnants of provenance area. CO 2 density in detrital quartz grains characterise the protolith of the sandstone as granite or metamorphic rock. The H 2O-NaCl fluids involved in the recrystallization processes at temperature-pressure of 430-350°C; 4.8 to 0.5 Kbars as constrained by fluid isochores of CO 2-H 2O and H 2O-NaCl inclusions and bulging and subgrain development during recrystallization processes. The re-equilibration of the primary fluid due to elevated internal and confining pressure is evident from features like ‘C’ shaped cavities, stretching of the inclusions, their migration and decrepitation clusters. The observed inclusion morphology revealed that the rocks were exhumed along an isothermal decompression path. [ABSTRACT FROM AUTHOR]

A detailed geological, geomorphological and landuse/landcover study has been carried in a small watershed of Himalaya by visual interpretation of FCC prepared from band 123 of ASTER satellite imagery. On the basis of interpretation and field check, major litounits identified in the study area include Lesser Himalaya conglomerate consisting of quartzite, granite, phyllite boulder and pebble, Middle Siwalik sandstone and Upper Siwalik boulder beds and valley fill with Doon gravel of Holocene age. Geomorphologically the study area is characterized by typical Himalayan topography with rugged terrain. Various landforms identified and recognized include, Doon Fan Gravel Terrace, Doon Fan Gravel Dissected hill, Sub Recent Fan Terrace, Moderately Dissected Structural Hill, Piedmont Dissected Slope, River Terrace, Channel Bar and River channel. Supervised classification of ASTER False Colour Composite (FCC) (123) shows that the major landuse category in the study area is agriculture while major landcover class is forest covered land. The study shows the effect of geology and geomorphology on the type of landuse and landcover in an active tectonic zone of the study area. [ABSTRACT FROM AUTHOR]

In this paper, microcrack patterns in a quartzite are quantified using fractal geometry based methods. Since the quartzite does not show a mesoscopic foliation, the fabric was recognized using anisotropy of magnetic susceptibility (AMS) analysis. Microcracks were investigated in thin sections prepared along the three principal planes of the AMS ellipsoid. Point load tests were performed on cores drilled parallel as well as perpendicular to the magnetic foliation. After experimental deformation, thin sections were prepared in two orientations - (a) parallel to the plane of failure (i.e., parallel to the direction of loading), (b) perpendicular to the plane of failure (i.e., perpendicular to the direction of loading), and microcrack patterns in these sections were investigated. The box-counting method of fractal analysis was first applied to microcracks traced from SEM images from each thin section of the experimentally undeformed as well as deformed samples to establish the fractal nature of the microcrack pattern. It was found that in thin sections perpendicular to the direction of loading, the box (fractal) dimension tends to marginally increase. This is inferred as a manifestation of the increase in complexity of the pattern. The software AMOCADO, which is based on the modified Cantor Dust method of fractal analysis, was applied to microcrack pattern from each thin section in order to quantify the pattern anisotropy. It is noted that the anisotropy significantly reduces in sections perpendicular to the loading direction. SEM data are presented to demonstrate that this reduction in anisotropy is on account of generation and/or growth of new cracks in random orientations. It is envisaged that the approach adopted in this investigation maybe useful in rock mechanics and mineral-resource applications in future. [ABSTRACT FROM AUTHOR]

Carbonate and calcareous-quartzite of Miri-Buxa Group in the Siang Window of Eastern Himalaya intruded by mafic rocks of gabbroic affinity. These intrusive rocks are low-Ti tholeiites (Ti/Y = 379−478; Nb/La = 0.99−1.88) and characterized by enriched LILE-LREE, depleted in HFSE with minor REE fractionation [(La/Yb) = 2.72−3.35)]. Geochemical behaviour of the incompatible trace elements with the rare earth elements abundances indicates their cogenetic nature and their emplacement in a continental rift tectonic environment. The liquidus olivine temperature of these mafic rocks ranges from 1262°C to 1380°C showing a gentle decrease of [Mg] with a steep increase of [Fe]. These charters thus imply that the rocks are either related to the extent of common source or fractionational crystallization of plagioclase and clinopyroxene from a single batch parental magma. Petrogenetic modeling of [Mg]-[Fe] and REE indicates that these mafic intrusives probably derived from a mantle source similar to komatiitic composition at moderate to high degree (8%-20%) of partial melting. [ABSTRACT FROM AUTHOR]

Pyrophyllite deposit at Madrangjodi is a large lensoidal massif overlain unconformably by Dhanjori quartzite and underlain by the parent Singhbhum granite (Phase - II). Pyrophyllite and quartz are the major minerals with minor to trace amounts of muscovite, chloritoid opaques and tourmaline. It is broadly divisible into lamellar, granular and schistose varieties. SiO (66.90-74.36%) and AlO (20.80-27.54%) are the major oxides. The major elements data indicate its derivation from Singhbhum granite with depletion of SiO and increment of AlO. Trace and REE data are discussed to corroborate its genesis. [ABSTRACT FROM AUTHOR]