Granite Gneiss Complex Research Articles

High Resolution Multispectral Satellite Data Interpretation and Limited Ground Checking: A Proxy for Geological Mapping and Uranium Exploration in Mahakoshal Fold Belt of Son Valley Area, Madhya Pradesh

Abstract: This research aims at integrating remote sensing data and field studies to prospect for uranium mineralisation in the Palaeoproterozoic Mahakoshal Group of rocks in the Son valley area, Central India. In present work, a revised geological map of Mahakoshal Fold Belt (MFB) bounded by Son-Narmada north fault (SNNF) and Son-Narmada south fault (SNSF) along Chorhut-Sidhi-Chitrangi sector falling in Sidhi, Rewa and Shahdol districts of Madhya Pradesh has been prepared based on interpretation of digitally enhanced satellite images. The satellite image interpretation is supported by limited field works, radioelemental measurements (eU, eTh and % K) of in-situ rocks by four channel Portable Gamma Ray Spectrometer (PGRS) and existing published geological maps of Geological Survey of India. In search for mineral potential areas, accurate and up-to-date geological maps are essential as it represent the most basic information for carrying out further exploration activities. However, available geological maps of MFB and sedimentary formations of Vindhayan Supergroup along SNNF and Chhotanagpur Granite Gneissic Complex (CGGC) and Gondwana Supergroup along SNSF available in public domain are discontinuous and multi-scaled. Optical bands of Landsat Enhanced Thematic Mapper Plus (ETM+) and Indian Remote Sensing (IRS) PAN of the study area were used in mapping lithological units, structural features and small intrusive bodies. Principal Component Analysis (PCA), Image Fusion, Linear Contrast Stretch, Histogram Equalisation and False Color Composite (FCC) of various band combination and ratio maps were performed in the digital image processing of geo-rectified satellite imageries. In analyzing and interpreting high resolution multi-spectral images, certain standard norms were employed to acquire information about litho-structural features such as topographic, geomorphic and tectonic facets. The main criteria are colour and tones, geomorphology, drainage patterns and vegetation anomalies. The processed Landsat ETM+ images were interpreted and classified to delineate detailed lithological units and structural features in order to update existing geological maps. To validate the prepared litho-structural map, ground survey was carried out along critical geological sections for checking the geological features like rocks, folds, faults, fractures and foliations. While comparing with the ground geological data to that obtained from the satellite imagery, it is observed that remote sensing interpreted litho-structural map is in a class with the ground observations. Various data sets such as unconformable geological contacts, fault breccias zone, lineaments and gamma ray spectrometric data (eU, eTh and % K) based on PGRS study were integrated and modelled using Geographical Information System (GIS) for identifying important prospective horizons for uranium mineralisation in the MFB of Son valley area. It is concluded that the revised large scale geological map is of practical use for not only for mapping of litho-structural architecture, but also in identifying potential areas for ‘vein –type’ uranium mineralisation along the structurally deformed zones of the SNNF, Asmi-Jiawan fault (AJF) and SNSF; and ‘unconformity- type’ of uranium mineralisation in the outliers of Jungel Group. The revised map and radiometric data acquired are useful in formulating exploration strategy for the ongoing uranium exploration in this area

Ruby–sapphire–spinel mineralization in marble of the middle and southern Urals: Geology, mineralogy, and genesis

Ruby and spinel occurrences hosted in marble on the eastern slope of the Urals are considered. Ruby- and spinel-bearing marble is a specific rock in granite-gneiss complexes of the East Ural Megazone, which formed at the Late Paleozoic collision stage of the evolution of the Urals. Organogenic marine limestone is the protolith of the marble. No relict sedimentary bedding has been retained in the marble. The observed banding is a secondary phenomenon related to crystallization and is controlled by flow cleavage. Magnesian metasomatism of limestone with the formation of fine-grained dolomite enriched in Cr, V, Ti, Mn, Cu, Zn, Ga, and REE took place at the prograde stage of metamorphism. Dedolomitization of rocks with the formation of background calcite marble also developed at the prograde stage. Mg-calcite marble with spinel and ruby of the first type formed in the metamorphic fluid circulation zone. Magnesian metasomatism with the formation of bicarbonate marble with ruby, pink sapphire, and spinel of the second type developed at the early retrograde stage. The formation of mica-bearing mineralized zones with corundum and spinel of the third type controlled by cleavage fractures is related to the pneumatolytic–hydrothermal stage. The data on ruby-bearing marble in the Urals may be used for forecasting and prospecting of ruby and sapphire deposits hosted in marble worldwide.

Mapping of groundwater potential zones in hard rock terrain using geoinformatics: a case of Kumari watershed in western part of West Bengal

Groundwater is one of the world’s most precious natural resources. But still now this valuable resource is largely unexploited for agricultural development in drought prone western region of West Bengal. In drought prone areas micro-watershed based development strategy may be considered as the best practice for integrated development. Keeping in view the above perspective, we select Kumari watershed of Purulia district, the westernmost and semi-arid district of West Bengal for better water resource management. Geologically the area consists of Chotanagpur granite gneiss complex while physiographically it is highly dissected pedimental landscape with lateritic upland and skeletal soil. As a result, cultivation of this area is predominantly mono-cropped and thus per hectare production is also low as compared to other regions of West Bengal. Supply of sufficient water resource in this region may offer more food security alternative to rain-fed subsistence farming. That’s why the present study has been carried out to evaluate the potential zones for groundwater targeting in Kumari watershed of Purulia district using an integrated remote sensing data, Survey of India topographical sheets and field verification. Hydro-geological features (geomorphological and geological units, slope, drainage density, lineaments density etc.) that influence groundwater occurrence were extracted and integrated to evaluate the hydro-geomorphological characteristics of the study area. Thematic maps of the extracted features were prepared with the help of ERDAS Imagine 9.0 and Arc-GIS 9.3 software. Weightage values were assigned to the different parameters according to their relative importance to groundwater potentiality and integrated through Geographic Information System environment. Finally on the basis of grid-wise theme weight and class weights the groundwater potential map was prepared by overlay the thematic layers.

Metallogeny of the North Atlantic Craton in Greenland

AbstractThe North Atlantic Craton (NAC) extends along the coasts of southern Greenland. At its northern and southern margins, Archaean rocks are overprinted by Palaeoproterozoic orogeny or overlain by younger rocks. Typical granite-greenstone and granite-gneiss complexes represent the entire Archaean, with a hiatus from ∼3.55–3.20 Ga. In the granulite- and amphibolite-facies terranes, the metallogeny comprises hypozonal orogenic gold and Ni-PGE-Cr-Ti-V in mafic-ultramafic magmatic systems. Gold occurrences are widespread around and south of the capital, Nuuk. Nickel mineralization in the Maniitsoq Ni project is hosted in the Norite belt; Cr and PGE in Qeqertarssuatsiaq, and Ti-V in Sinarsuk in the Fiskenæsset complex. The lower-grade metamorphic Isua greenstone belt hosts the >1000 Mt Isua iron deposit in an Eoarchaean banded iron formation. Major Neoarchaean shear zones host mesozonal orogenic gold mineralization over considerable strike length in South-West Greenland. The current metallogenic model of the NAC is based on low-resolution data and variable geological understanding, and prospecting has been the main exploration method. In order to generate a robust understanding of the metal endowment, it is necessary to apply an integrated and collective approach. The NAC is similar to other well-endowed Archaean terranes but is underexplored, and is therefore likely to host numerous targets for greenfields exploration.

Petrography, Geochemistry and Rb-Sr Geochronology of the Basement Granitoids from Umthongkut Area, West Khasi Hills District, Meghalaya, India: Implications on Petrogenesis and Uranium Mineralization

Abstract The basement granitoids from Umthongkut, West Khasi Hills district, Meghalaya is exposed in a very small area (1.5 km x 0.5 km) and unconformably overlain by Mahadek sandstone of upper Cretaceous age and successively followed by rocks of Tertiary age. Megascopically, granitoids are leucocratic, mesocratic to mild melanocratic and differ in texture and mineral abundance without any definite contact relation in field. The leucocratic granitoid is medium-grained, designated as granite (syenogranite and monzogranite) with appreciable content of biotite and garnet and has peraluminous to mild metaluminous character (mol. Al2O3/mol. CaO+Na2O+K2O= 0.9-1.17). However, mesocratic granitoid is relatively fine-grained, identified as quartz monzonite with abundant biotite, minor hornblende and opaque like magnetite, ilmenite, anatase, pyrite and chalcopyrite and metaluminous to mild peraluminous (mol. A/CNK=0.76-1.02) in nature. The presence of characteristic minerals and textural replacement features point towards S-type signature for granite and I –type for quartz monzonite. On the other hand, mixed S and I-type characters are observed in geochemical plot of SiO2 vs. A/CNK. The coexistence of granite and quartz monzonite with former being more evolved, S-type signature and presence of garnet with biotite suggests that the granite appears to be generated from melting of lower crustal source of monzonitic composition. The Rb-Sr dating is also attempted and the errorchron age of 1130±53 with low initial 87Sr/86Sr ratio of 0.7063±0.0011Ma appears to be the emplacement age for these coexisting phases of granitoid. Considering the Meghalaya plateau being northeastern extension of Chhotanagpur granite-gneiss complex (CGGC), the calculated age for the studied samples corresponds to the 1200-1000 Ma. which is defined as fourth tectono-magmatic thermal event of CGGC. Interestingly, these granitoids are considered as the probable source for uranium in the sandstones of Mahadek Formation of Cretaceous age hosting ore grade uranium mineralization at Umthongkut,

Geochemistry of biotites and host granitoid plutons from the Proterozoic Mahakoshal Belt, central India tectonic zone: implication for nature and tectonic setting of magmatism

The northern part of the central India tectonic zone (CITZ) is occupied by the Proterozoic Mahakoshal Belt, which is mainly comprised of granitoids and volcano-sedimentary lithounits. The granitoids (ca. 1880–1710 Ma) are exposed as small circular to elliptical-shaped, stock-like intrusive bodies, such as Nerueadamar granitoids (NG), Tumiya granitoids (TG), Jhirgadandi granitoids (JG), Dudhi granite gneiss (DG), Raspahari granitoids (RG), Katoli granitoids (KG), and Harnakachar granitoids (HG), collectively forming the granite gneissic complex (GGC). The geochemistry of biotites, host granitoids, and enclaves from these plutons has been investigated in order to understand the redox condition and likely tectonic affinity of host granitoids. The Al2O3–MgO–FeOt contents and operated elemental substitution in biotites strongly suggest the diverse nature of host magmas such as calc-alkaline, metaluminous (I-type), peraluminous (S-type), and transitional between I- and S-types, which appear to have formed in subduction zone and syn-collisional tectonic settings. The transitional (I-S)-type granitoids inferred based on biotite compositions, however, represent both metaluminous (HG) and peraluminous (DG and KG) granitoids in terms of whole-rock molar A/CNK (Al2O3/CaO + Na2O + K2O) ratios. Ages of granitoid magmatism and its field association with contemporaneous volcano-sedimentary lithounits clearly mark the post-collisional tectonic setting, which contradicts the subduction-related tectonic setting inferred from biotites of JG and microgranular enclave (JE) hosted in JG. Whole-rock major and trace elements broadly suggest the existence of collision tectonics during the formation of granitoid plutons. The JG, KG, and DG contain a bt-Kf-mag-qtz assemblage, and their parental magmas evolved under moderate oxidizing environments (ƒO2 = −12.03 to −13.27 bars). On the other hand, RG (bt-gt-Kf-pl-qtz), NG (bt-ms-Kf-pl-qtz), and TG (bt-ms-Kf-pl-qtz) represent pure crustal-derived magmas evolved in strongly reducing conditions formed under a syn-collisional tectonic setting as evident from their mineral assemblages and biotite and whole-rock compositions. Granitoid plutons of the Mahakoshal Belt were most likely formed during amalgamation of the Columbian supercontinent.

Chapter 5 Controls on sedimentation in Indian Palaeoproterozoic basins: clues from the Gwalior and Bijawar basins, central India

Abstract Overlying Archaean Bundelkhand Granite Gneiss Complex, the Gwalior and Bijawar Groups of rocks represent two Palaeoproterozoic basin successions which, despite their common sediment provenance and analogous rift-related tectonic setup, record more dissimilarity in their sedimentation pattern than similarity. Whereas early sedimentation in the Gwalior Basin is clastic, the early Bijawar sedimentation is dominantly chemogenic (limestone and chert) except for an early, restricted volcano-clastic record. Although both of the basins record syn-depositional volcanic/volcaniclastic event(s) in the form of occurrence of basaltic and basaltic–andesite sills encased within their respective basin fills, the occurrence of iron formation in the later part of Gwalior sedimentation history and its absence in the Bijawar succession is related to variable oxidation conditions in the water columns of the two basins. Rising sea-level and upwelling on the continental margins of these two rift-related basins possibly generated different water chemistries; these allowed the deposition of iron formation in the Gwalior Basin and phosphorite in the Bijawar Basin. Effects of post-depositional digenetic re-crystallization are noticed within both iron formation and phosphorite deposits present in the basin successions.

Invisible gold occurrence within the quartz reef pyrite of Babaikundi area, North Singhbhum fold-and-thrust belt, Eastern Indian Shield: Evidence from petrographic, SEM and EPMA studies

The Mesoproterozoic metasedimentary rocks of Chandil Formation belong to the northern part of Singhbhum Crustal Province, eastern India. The Chandil Formation lies within the North Singhbhum fold-and-thrust belt and is demarcated at its southern margin by the Dalma volcano-sedimentary belt. Tamar-Porapahar Shear Zone (TPSZ) separates the Chandil Formation from the Meso/Neoproterozoic Chhotanagpur Granite Gneissic Complex (CGGC) at its northern boundary. The area is characterized by quartz-mica-sericite-schist, quartzite, amphibolites and carbonaceous phyllites and is ubiquitously traversed by mineralized quartz reefs/veins. The field relationships and the petrographic characteristics of the lithounits of Chandil Formation indicate evidence of multi-phase deformations, exhibited by the presence of S–C fabric, S1–S2 planes of schistosity, alternate layers of coarse and thin quartz veins. The gold mineralization in the study area occurs along the east–west oriented Babaikundi-Birgaon axis, which has been established as a sheared/fractured contact running parallel to the Tamar Porapahar Shear Zone lying to the north. Gravity, magnetic, resistivity and induced polarization (IP) survey across the Babaikundi-Birgaon axis indicates the presence of sheared/fractured contact and sulfide mineralization. The gold mineralization within the area is confined to the quartz reef along the contact of mica schist and ambhibolites. Ore minerals observed in the area are chalcopyrite, pyrite, pyrrhotite, arsenopyrite and sphalerite. The majority of the sulfide mineralization is associated with the ferruginous quartz veins. Gold occurs in two distinct forms, as lodes/nuggets and as invisible gold within the pyrite mineralization.Field observations, reflected and transmitted light microscopic study, SEM analysis and electron probe micro analyzer (EPMA) were used to give a brief account of the mineral chemistry and presence of different forms of gold (including the first report of invisible gold within North Singhbhum fold-and-thrust Belt). The occurrence of gold in the crystal lattice of the pyrite may be attributed to the substitution and replacement of Fe ion within the pyrite aided by the hydrothermal activity.

Geochemical constraints on the evolution of mafic and felsic rocks in the Bathani volcanic and volcano-sedimentary sequence of Chotanagpur Granite Gneiss Complex

The Bathani volcanic and volcano-sedimentary (BVS) sequence is a volcanic and volcano-sedimentary sequence, best exposed near Bathani village in Gaya district of Bihar. It is located in the northern fringe of the Chotanagpur Granite Gneiss Complex (CGGC). The volcano-sedimentary unit comprises of garnet-mica schist, rhyolite, tuff, banded iron formation (BIF) and chert bands with carbonate rocks as enclaves within the rhyolite and the differentiated volcanic sequence comprises of rhyolite, andesite, pillow basalt, massive basalt, tuff and mafic pyroclasts. Emplacement of diverse felsic and mafic rocks together testifies for a multi-stage and multi-source magmatism for the area. The presence of pillow basalt marks the eruption of these rocks in a subaqueous environment. Intermittent eruption of mafic and felsic magmas resulted in the formation of rhyolite, mafic pyroclasts, and tuff. Mixing and mingling of the felsic and mafic magmas resulted in the hybrid rock andesite. Granites are emplaced later, cross-cutting the volcanic sequence and are probably products of fractional crystallization of basaltic magma. The present work characterizes the geochemical characteristics of the magmatic rocks comprising of basalt, andesite, rhyolite, tuff, and granite of the area. Tholeiitic trend for basalt and calc-alkaline affinities of andesite, rhyolite and granite is consistent with their generation in an island arc, subduction related setting. The rocks of the BVS sequence probably mark the collision of the northern and southern Indian blocks during Proterozoic period. The explosive submarine volcanism may be related to culmination of the collision of the aforementioned blocks during the Neoproterozoic (1.0 Ga) as the Grenvillian metamorphism is well established in various parts of CGGC.

Estimation of depth extent of Gangam-Peruru complex of Eastern Dharwar Craton (EDC) from aeromagnetic data

A high-intensity aeromagnetic anomaly zone located in the region of Gangampalli-Peruru with an amplitude range of 500–1000 nT in the midst of peninsular granite-gneissic complex in a part of the Eastern Dharwar Craton (EDC) is associated with quartz monzodiorite with abundant titanite, Zr, and REE elements. This zone is situated between the eastern part of the Closepet granite (2513 Ma) and western part of the Ramagiri schist belt (2614 Ma). Spectral analysis and modeling of the aeromagnetic anomaly field of the Gangampalli-Peruru complex has been carried out to estimate the thickness of the complex. The analysis has yielded an average thickness ranging from 1700–2250 m.

Development of concave-face boudin in Chhotanagpur Granite Gneiss Complex of Jasidih-Deoghar area, eastern India: Insight from finite element modeling

With the help of 2D-finite element modeling the present study analyses the role of syntectonic migmatisation on the development of concave-face boudins within amphibolite dykes in Chhotanagpur Granite Gneiss Complex of Jasidih-Deoghar area, eastern India. Amphibolitic bands embedded in quartzofeldspathic gneiss show concave-face boudins with varied face geometries, resulted due to rheological changes during syntectonic migmatisation. Detailed study reveals that due to couple effect of H2O infiltration and potassium (K+)-metasomatism associated with the invasion of pegmatitic fluid, pyroxene converted to amphibole and later to biotite at the marginal part of the amphibolitic bands and especially, near the separation zone of boudin. In this study, three types of models are prepared to simulate three different patterns of syntectonic rheological changes that can best explain the features observed in the field. Type I is a symmetric rim model representing equal amount of rheological changes in all directions of a rectangular boudin object. Other two are asymmetric rim models (Type II and Type III) with different amount of rheological changes along length and width of the boudin block. The analysis also takes into account the effects of rate of syntectonic rheological changes (D). The study reveals that the pattern and rate of rheological changes have strong influences on the development of concave-face boudin. Type I model produces barrel-shaped fish-mouth boudin with extremely sharp corners, whereas Type III model produces more lensoid shape with relatively tighter fish mouth. For all types of model, U-shaped concave-face boudin develops at lower rate of rheological changes and the face geometry gradually transforms to V-shape with increasing the rate. The progressive change of face curvature (FC), exterior curvature (EC) and aspect ratio (AR) depends on the timing of rheological inversion during progressive deformation.

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.

Genesis of the Proterozoic Mangabeira tin–indium mineralization, Central Brazil: Evidence from geology, petrology, fluid inclusion and stable isotope data

The Mangabeira deposit is the only known Brazilian tin mineralization with indium. It is hosted in the Paleo- to Mesoproterozoic Mangabeira within-plate granitic massif, which has geochemical characteristics of NYF fertile granites. The granitic massif is hosted in Archean to Paleoproterozoic metasedimentary rocks (Ticunzal formation), Paleoproterozoic peraluminous granites (Aurumina suite) and a granite–gneiss complex. The mineralized area comprises evolved Li-siderophyllite granite, topaz–albite granite, Li–F-rich mica greisens and a quartz–topaz rock, similar to topazite. Two types of greisens are recognized in the mineralized area: zinnwaldite greisen and Li-rich muscovite greisen, formed by metasomatism of topaz–albite granite and Li-siderophyllite granite, respectively. Cassiterite occurs in the quartz–topaz rock and in the greisens. Indium minerals, such as roquesite (CuInS2), yanomamite (InAsO4·2H2O) and dzhalindite (In(OH3)), and In-rich cassiterite, sphalerite, stannite group minerals and scorodite are more abundant in the quartz–topaz rock, and are also recognized in albitized biotite granite and in Li-rich muscovite greisen. The host rocks and mineralized zones were subsequently overprinted by the Brasiliano orogenic event.Primary widespread two-phase aqueous and rare coeval aqueous-carbonic fluid inclusions are preserved in quartz from the topaz–albite granite, in quartz and topaz from the quartz–topaz rock and in cassiterite from the Li-rich muscovite greisen. Eutectic temperatures are −25°C to −23°C, allowing modeling of the aqueous fluids in the system H2O–NaCl(–KCl). Rare three-phase H2O–NaCl fluid inclusions (45–50wt.% NaCl equiv.) are restricted to the topaz–albite granite. Salinities and homogenization temperatures of the aqueous and aqueous-carbonic fluid inclusions decrease from the topaz–albite granite (15–20wt.% NaCl equiv.; 400°C–450°C), to the quartz–topaz rock (10–15wt.% NaCl equiv.; 250°C–350°C) and to the greisen (0–5wt.% NaCl equiv.; 200°C–250°C). Secondary fluid inclusions have the same range of salinities as the primary fluid inclusions, and homogenize between 150 and 210°C.The estimated equilibrium temperatures based on δ18O of quartz–mica pairs are 610–680°C for the topaz–albite granite and 285–370°C for the Li-rich muscovite greisens. These data are coherent with measured fluid inclusion homogenization temperatures. Temperatures estimated using arsenopyrite geothermometry yield crystallization temperatures of 490–530°C for the quartz–topaz rock and 415–505°C for the zinnwaldite greisens. The fluids in equilibrium with the topaz–albite granite have calculated δ18O and δD values of 5.6–7.5‰ and −67 to −58‰, respectively. Estimated δ18O and δD values are mainly 4.8–7.9‰ and −60 to −30‰, respectively, for the fluids in equilibrium with the quartz–topaz rock and zinnwaldite greisen; and 3.4–3.9‰ and −25 to −17‰, respectively, for the Li-rich muscovite greisen fluid. δ34S data on arsenopyrite from the quartz–topaz rock vary from −1.74 to −0.74‰, consistent with a magmatic origin for the sulfur. The integration of fluid inclusion with oxygen isotopic data allows for estimation of the minimum crystallization pressure at ca. 770bar for the host topaz–albite granite, which is consistent with its evolved signature.Based on petrological, fluid inclusion and isotope data it is proposed that the greisens and related Mangabeira Sn–In mineralization had a similar hydrothermal genesis, which involved exsolution of F-rich, Sn–In-bearing magmatic fluids from the topaz–albite granite, early formation of the quartz–topaz rock and zinnwaldite greisen, progressive cooling and Li-rich muscovite greisen formation due to interaction with meteoric water. The quartz–topaz rock is considered to have formed in the magmatic-hydrothermal transition. The mineralizing saline and CO2-bearing fluids are interpreted to be of magmatic origin, based on the isotopic data and paragenesis, which has been documented as characteristic of the tin mineralization genetically related to Proterozoic within-plate granitic magmatism in the Goias Tin Province, Central Brazil.

Noble metal-graphite mineralization: A comparative study of the carbonaceous granite-gneiss complex and shales of the Russian Far East

A new noble metal-graphite mineralization has been revealed in the Ruzhino amphibolite-facies rocks of the northern Khanka block. It is characterized by Au and PGE (platinum group elements) contents (up to tens g/t, Pt>Au) as high as those in world-class deposits hosted by sedimentary and magmatic rocks, but is distinguished from them by isotopic composition of carbon, hydrogen and oxygen, all suggesting a distinct mantle contribution (δ13СVPDB from −8.5 to −10.5‰ in graphite, δDVSMOW from −82.5 to −106.7‰ and δ18OVSMOW from 8.2 to 10.1‰ in biotite). The Ruzhino-type mineralization is highly resistant to common chemical treatments, so that detection of their metals requires that some special methods be developed. Atomic Absorption Spectrophotometry and Inductively Coupled Plasma Mass Spectrometry following severe chemical treatments and ignition at 600–650°C, as well as Ion Mass Spectrometry allowing a direct detection of elements in solid materials were employed in this study. These methods increased noble-metal contents of the graphitized rocks compared to standard analyses including a conventional fire assay. In addition, electron microscopy surveys discovered extremely diverse native-metal and intermetallic complexes with C, O, Cl, F, REE and other elements. The microinclusions, however, represent a minor part of the mineralization. Major constituents seem to form carbonaceous nanocompounds invisible under a microscope. These graphite-based nanocomplexes, which are especially developed in the case of Pt, seem to be responsible for the highly resistant character of the Ruzhino mineralization. They also may be present in the latent form among the common Au±PGE ores hosted by carbonaceous shales like those we studied in the close vicinity of the Ruzhino amphibolite-facies rocks and in the northeastern Bureya–Jiamusi terrane.

A review of the ∼1600 Ma sedimentation, volcanism, and tectono-thermal events in the Singhbhum craton, Eastern India

The Palaeoproterozoic–Mesoproterozoic transition (∼1600 Ma) is a significant event in the Earth history as a global thermal perturbation affected the pre-1600 Ma landmasses. Like other cratonic blocks of the world, lithospheric thinning, sedimentation, magmatism, metamorphism and crustal melting/anatexis are associated with this significant geological event in the Singhbhum cratonic province of India. This paper is a review of sedimentological, magmatic and tectono-thermal events in the Singhbhum craton at ∼1600 Ma. The Palaeo-Mesoproterozoic sedimentation and volcanism in the Singhbhum craton took place in a terrestrial intracontinental rift setting. The available geochronological data are indicative of late Palaeoproterozoic to Neoproterozoic tectono-thermal events in the Chhotanagpur Granite Gneissic Complex (CGGC), an east–west trending arcuate belt of granite gneisses, migmatites and metasedimentary rocks. A detailed multidisciplinary geo-scientific investigation of the Dalma volcanic belt and the area to its north (Chandil Formation) and further north in CGGC will enable us to constrain the extant surface processes and crust-mantle interactions, the collision events between the North and South Indian cratonic blocks, and the position of India in the Columbia supercontinent.

Metamorphic evolution of the Chotanagpur Granite Gneiss Complex of the East Indian Shield: current status

Abstract Geological information on the Chotanagpur Granite Gneiss Complex (CGGC) has been reviewed with a view to: (a) identifying the different metamorphic episodes; (b) developing an event stratigraphy in the high-grade blocks; and (c) correlating the different metamorphic episodes with the globally extensive orogenic processes. Integrating the existing geological information, the geological evolution of the high-grade block of the CGGC has been divided into four stages associated with four distinct metamorphic events ( M I − M IV ). The earliest metamorphic event ( M I ) that is recorded in granulite enclaves in the regionally extensive felsic gneisses culminated in ultrahigh temperatures (>900 °C at c . 5–8 kbar) at around 1.87 Ga. In the second stage, voluminous felsic magmas were intruded – the M I granulites – and were metamorphosed to form migmatitic felsic gneisses ( M II ) within about 1.66–1.55 Ga. The third stage witnessed intrusions of a suite of anorthosite and porphyritic granitoids ( c . 1.55–1.51 Ga), followed by high-grade metamorphism (700±50 °C, 6.5±1 kbar, M III ) during approximately 1.2–0.93 Ga. The fourth stage ( M IV ) is marked by the intrusion of a suite of mafic dykes, followed by infiltration-driven metamorphism (600–750 °C at 7±1) during 0.87–0.78 Ga. The proposed metamorphic events have been correlated with the supercontinental cycles in the Proterozoic time.

Reactivation of basement: example from the Anasagar Granite Gneiss Complex, Rajasthan, western India

Abstract Amidst the Meso- to Neoproterozoic South Delhi Fold Belt (SDFB) of Rajasthan, India, a sheet-like body of megacrystic Anasagar Granite Gneiss (AGG) embedded in a supracrustal unit consisting of metapelites, quartzite and calc gneiss is exposed. Detailed analyses of mesoscopic and microscopic structures identify four phases of deformation. Lithological relationships coupled with U–Pb dates of zircon indicate that the protolith of the AGG was emplaced within the supracrustal unit during D 1 folding at approximately 1.85 Ga. This event is significantly older than the age of volcanism in the SDFB (0.99 Ga) but probably synchronous with Aravalli Orogeny. Thrusts associated with the easterly-vergent D 2 folds have a ramp–flat geometry and are refolded by coaxial D 3 folds. The petrology of the metapelites indicates that porphyroblasts of staurolite and/or garnet were formed as a function of bulk-rock composition between D 1 and D 3 folding, at the time of the culmination of metamorphism (5.7±1.5 kbar, 560±50 °C). Combining the petrological and structural attributes, it is proposed that the AGG and its enveloping supracrustals might represent the basement of the Delhi Supergroup, which was folded, thrusted and domed up during the South Delhi Orogeny. The cause of the thermal perturbation that triggered the growth of the porphyroblasts in the metapelites is explored.

Early Precambrian granite-gneiss complexes in the Central Aldan Shield

The central portion of the Aldan Shield hosts very widely spread Archean and Early Proterozoic granitoids, much of which are granitegneisses. Geochemical lines of evidence, data on inclusions in miner� als, and Sm-Nd isotopic geochemical data suggest that the protoliths of granitegneisses in the central part of the Aldan Shield were granitoids that had various composition, age, and were derived from distinct sources and under different parameters and were then emplaced in different geodynamic environments. The grani� toids belong to at least two types of different composition that occur within spatially separated areas. The pro� toliths of granitegneisses in the western part of the Western Aldan Megablock and the junction zone of the Chara-Olekma and Aldan geoblocks (granitegneisses of type I) had the same age and affiliated to the same associations as the withinplate granitoids of the Nelyukinskii Complex. Their parental melts were derived at 2.4-2.5 Ga by the melting of Archean tonalite-trondhjemite orthogneisses of the Olekma and Aldan com� plexes. The protolith of granitegneisses in the east ern portion of the Western Aldan Megablock (granite� gneisses of type II) can be subdivided into two groups according to their composition: granitoids with geochemical characteristics of subductionand collisionr elated rocks. The protoliths of the typeII granite� gneisses with geochemical characteristics of subduction granitoids were produced simultaneously with the development of the Fedorovskaya island arc (at 2003-2013 Ma), whereas the protoliths of the typeII gran� itegneisses with geochemical characteristics of collisio n granitoids were formed in the course of accretion of the Fedorovskaya island arc and the Olekma-Aldan continental microplate at 1962-2003 Ma, via the melt� ing of magmatic rocks of the Fedorovskaya unit and older continental crustal material.

Lower proterozoic metapelites in the northern Yenisei Range: Nature and age of the protolith and the behavior of material during collisional metamorphism

The variable P-T metamorphic conditions studied in the Fe-Al metapelites of the Karpinskii Range Formation are regarded as typical of collision-related metamorphism in the trans-Angara part of the Yenisei Range. Recently obtained geochronologic (SHRIMP-II U-Pb zircon dating) and geochemical data on the distribution of major and trace elements are used to reproduce the composition of the protolith, the facies conditions under which it was formed, the tectonic setting, and the age of the eroded rocks. The metapelites are determined to be redeposited and metamorphosed material of Precambrian kaolinite-type weathering crusts of predominantly kaolinite-illite-montmorillonite-quartz composition. The protolith of the rocks was formed via the erosion of Lower Proterozoic granite-gneiss complexes of the Siberian craton (dated mainly within the range of 1962–2043 Ma) and the subsequent accumulation of this material in a continent-marginal shallow-water basin in a humid climate and tectonically calm environment. These results are consistent with data of lithologic-facies analysis and geodynamic reconstructions of the Precambrian evolution of geological complexes in the Yenisei Range. Mass-transfer analysis with the use of the evaluated rock compositions and calculated chemical reactions indicates that the differences in the REE patterns of metapelites from distinct zones can be explained mostly by the chemical heterogeneity of the protolithic material and, to a lesser extent, by metamorphic reactions at a pressure increase.

Evolution of granulite enclaves and associated gneisses from Purulia, Chhotanagpur Granite Gneiss Complex, India: Evidence for 990–940 Ma tectonothermal event(s) at the eastern India cratonic fringe zone

Migmatitic quartzofeldspathic gneisses at Purulia, Chhotanagpur Granite Gneiss Complex (CGGC) contains layers and enclaves of high Mg–Al granulite and two-pyroxene granulites. Petrographic, geothermobarometric and pseudosection analyses of the high Mg–Al granulite reveal a strongly decompressive (Δ P = 6 kbar) retrograde trajectory after attaining the peak at 870 °C, 11 kbar. The metamorphic evolution ensued through partial melting of biotite-bearing assemblage. Texturally-constrained monazite grains yield population age of ca. 990–940 Ma which might bracket the timing of decompressive metamorphism in the high Mg–Al granulite broadly coinciding with the age of anatexis of the host gneisses. Associated mafic granulites underwent similar metamorphic evolution, but their contrasting bulk chemistries are responsible for mineralogical and textural variability. Formation and stabilization of garnet in one bulk composition of mafic granulite and breakdown of garnet in the other could be reconciled as products two different P– T segments of same metamorphic evolutionary history. Discrete population of older monazite ages (ca. 1800 Ma) in the host gneisses possibly implies variable degrees of inheritance. It is proposed that the ca. 990–940 Ma tectonothermal event caused extensive partial melting in the lower crust of the eastern Indian cratonic fringe zone. Widespread occurrence of ca. 1000–900 Ma metamorphism in the CGGC can be correlated with those in the Rayner–Eastern Ghats Belt in the Indo-Antarctic sector. All these areas experienced high-grade metamorphism as a result of Indo-Antarctic collision during the assembly of Rodinia.