013952   Jennings C M H;Smithson N K (NO, SouthernEra Resource Limited, 33, Younge Street, Suite 1040, Toronto, Ont, M5E 1S9, Canada) : Exploration context for diamonds. J Geophys 1999, 20(4), 241-52.

World natural diamond production for 1997 is estimated to be approximately 117 million carats. Of 7000 known kimberlite/lamproite occurrences, less than 60 have been mined with only about 15 major producers (0.21% of all pipes). Only nine mines that produce more than 3 million carats per annum have been discovered since 1950. Exploration strategy, world production, sizes of pipes, quality and value of diamonds, mining, milling and economics of diamond mining are discussed. An overview is given of area selection methods; exploration methods (indicator sampling, geophysical techniques); mineral chemistry and petrographic techniques; use of microdiamonds; initial and advanced evaluation of diamond pipes and marketing of diamonds.

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013951   Hossain D (Department of Geological Sciences, Jahangirnagar University, Savar, Dhaka, Bangladesh) : Application of common-depth-point shooting in the Surma basin, Bangladesh : a case study of the Rashidpur structure. J Geol Soc India 2000, 55(2), 149-56.

Analysis of the available seismic data from the Rashidpur anticlinal structure in the Surma basin, Bangladesh, shows that there are only a few interfaces that may generate significant reflections (medium category reflectors) down to the depth of four km, while the rest correspond to the category of weak reflectors. The relative amplitudes of different types of multiple events reveal that only 1st order surface multiples and peg leg multiples may possess amplitudes that can be detected on a seismogram. It has been concluded that the application of common-depth-point (CDP) shooting in the Surma basin should be directed towards not only enhancing signal-to-noise ratio (SNR), but also obtaining precise seismic velocity information.

013950   Haggerty S E (Department of Geosciences, University of Massachusetts, Amherst, Mass 01003 USA) : Tectonic settings and diamond productivity of kimberlite-clan rocks. J Geophys 1999, 20(4), 139-54.

Geological and tectonic settings of kimberlite-clan rocks (KCRs), defined as alkali ultramafic intrusives that are volatile and light rare-earth-element enriched, and are capable of transporting mantle xenoliths and diamonds from depths in excess of 660 km, are reviewed from the West African Craton, the Congo Craton, the Kaapvaal Craton, the Kimberley Craton (NW Australia), the Sino-Korean Craton, the Siberian Platform, and for cratons in Brazil, the USA, Canada, and India. Diamond deposits are in Archean and Proterozoic cratons that have lithospheric roots (keels) to depths of at least 200 km, and the optimum conditions for diamond formation and diamond preservation are low heat flows in tectonically stable cratons. Delamination of diamondiferous keels and thermochemical interaction appear to be major influences in controlling the diamond productivity of KCRs. There is a consistent pattern of crustal lineaments, and lineament controls on KCR diatremes by long lived reactivated faults and mega-shear systems in all of the diamond provinces reviewed. This pattern, as well as the clustering of 10-100 pipes in all cratons, implies that successful access of explosive volcanism in the crust, without the combustion of diamond, requires long term preconditioning of the crust but rapid access of KCRs through conduits and along deeply penetrating faults that may reach the upper mantle.

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013949   Gadgil S (Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore-560 012) : Monsoon-cean coupling. Curr Sci 1999, 78(3), 309-22.

Indian monsoon is maintained by propagation of convective systems of synoptic (lows, depressions, etc.) and planetary scale (tropical convergence zones) from the warm tropical oceans, onto the heated subcontinent. As a result, the monsoon variability on sub-seasonal scales (between wet and dry spells) and on interannual scales (good monsoons and droughts) is linked to variation of the convective systems over the ocean, where variability in turn depends on the sea surface temperature through complex relationship. The nature of this relationship and the mechanisms suggested for understanding it are discussed. It is suggested that for further insights into monsoon-cean coupling detailed observations particularly over the Indian seas with new satellites and special observational experiments are essential.

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013948   Chandrasekharam D;Vinod K C (Department of Earth Sciences, Indian Institute of Technology, Powai, Mumbai-400 076) : Clinopyroxenite xenoliths from the deccan trap lavas of Kutch and Mumbai. Curr Sci 2000, 78(5), 607-10.

Only a few occurrences of mantle xenoliths have been reported in the Deccan basalt province. These include the spinel peridotite and spinel lherzolite from Kutch and clinopyroxenite (with minor olivine) from Murud-Janjira coast. Reports hitherto unknown clino-pyroxenite xenoliths from Kutch and Powai. The Kutch xenoliths are accidental and the Powai Xenoliths are cognate. The Kutch clinopyroxenite xenoliths appear to have been formed due to the reaction between the mantle, containing olivine and ortho-pyroxene, and carbonated alkaline magma at about 1100°C and 17 kb pressure. The Powai xenolith represents cumulates of clinopyroxenes in the magma chamber which were picked up and brought up by a subsequent eruption.

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013947   Chandrasekaran C G;Ramanathan S (Department of Geology, Presidency College, Madras-600 005) : Granitic pegmatites from transition zone of amphibolite-granulite metamorphic belts of Krishnagiri, Dharmapuri district, Tamil Nadu. Indian J Geochem 1998, 13, 17-23.

Krishnagiri area, lying in the transition zone between the amphibolite and granulite metamorphic terrains, is composed of mainly grey granitic gneisses which are traversed profusely by pegmatites of different shapes and sizes. The pegmatites have been classified as interior, homogeneous and complex types. The minerals, found in the order of decreasing abundance, are quartz, orthoclase, plagioclase, biotite, muscovite and apatite. The emplacement of pegmatites is structurally controlled. The presence of appreciable amounts of biotites is believed to be due to the presence of high water content in the original pegmatite fluid. It is suggested that the different types of pegmatites composed of orthoclase and plagioclase are formed owing to overlapping influx of potash-rich and soda-rich solutions within the same range of time.

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013946   Bhatt N (Department of Geology, Faculty of Science, M.S. University of Baroda, Vadodara-390 002) : Lithostratigraphy of the Neogene-Quaternary deposits of Dwarka-Okha area, Gujarat. J Geol Soc India 2000, 55(2), 139-48.

Formal lithostratigraphic classification is suggested for the Neogene-quaternary sediments of the Dwarka-Okha (Okhamandal) area. They are classified into three formations Viz., Gaj, Dwarka, and Chaya. The Gaj Formation is divided into Ashapura Clay Member and Ranjitpur Limestone Member and it ranges from Lower to Middle Miocene in age. The disconformably overlying Dwarka Formation is of Middle Miocene to Lower Pliocene age and divisible into three members viz., Positra Limestone, Shankhodhar Sand-Clay and Kalyanpur Limestone. The quaternary deposits unconformably overlie this unit and are classified into Chaya Formation that consists of Okha Shell Limestone and Aramda Reef Members. These are Middle to Upper Pleistocene in age.

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013945   Balakrishna Rao N (Geological Survey of India, , Southern Region, Hyderabad) : Appraisal of the structural set-up of Wajrakarur and Lattavaram areas using potential field and radiometric data. J Geophys 1999, 20(4), 205-15.

Geophysical data comprising gravity, magnetic vertical field (VF), aeromagnetic and potassium data have been studied and interpreted to deduce the structures which might have played role in the emplacement of kimberlites. The processed maps of gravity and the synthesis of different data sets has helped in correlation and delineation of structures. A careful look of the structural setup near the known kimberlite pipes reveals very good similarity and it can be said that all the pipes in Wajrakarur and Lattavaram areas are invariably located at the junction or very close to the intersection of near N-S and near E-W fault/fracture system. This aspect is reflected both in regional and detailed scale maps. Besides the well established `a posteriori' approach i.e. extending the geophysical signatures corresponding to the structures near the known kimberlite pipes to the new areas, other features like structural breaks, proximity of circular features, and the bulge in adjacent gravity contour pattern representing probable zones of dilation are some of the criteria for identification of target areas. The aeromagnetic and potassium maps very well corroborate the inferences drawn from the potential field and the derivative maps.

012888   Valdiya K S (Geodynamics Unit, Jawaharlal Nehru Centre for Advanced Scientific Rese, , Bangalore-560 064) : Reactivation of faults, active folds and geomorphic rejuvenation in eastern Kumaun Himalaya : wider implication. Indian J Geol 1999, 71(1-2), 53-63.

Almora Thrust, which has placed Early Proterozoic crystalline rocks on Later Proterozoic sedimentary succession in Kumaun, has been reactivated in the Late Quaternary as a consequence of crustal shortening in the Lesser Himalayan terrain. Also affected by neotectonic movements are faults branching off from or parallel to the Almora Thrust. Not only has the terrain been spectacularly uplifted along these faults, but also its old mature landscape resurrected and considerably rejuvenated. This is evident from several levels of topographical benches on gentler slopes representing surfaces of erosion, convexity in steep slopes of gorges cut in wider valleys having gentler upper slopes, and entrenched meanders followed by abrupt localized narrowing of wider channels of mature streams in the proximity of active faults. Late Quaternary movements on faults resulted in ponding of streams and rivulets and development of lakes in fluvial regime and their eventual disappearance. The palaeolakes are represented by flat stretches made up of clay and mud with granule-size flat-pebble conglomerate within otherwise very rugged terrains. It is seen that between the projecting promontories at the two extremities of the Peninsular Indian plate, it is the middle segment of the Himalayan arc where compression and tectonic deformation have been comparatively mild and denudation protracted, which is exhibiting conspicuous geomorphic rejuvenation. The rate of uplift has been particularly faster in the Quaternary time. The compression and resultant uplift of the Himalaya is related to intraplate subduction of the Indian plate under the Himalaya.

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012887   Thamban M (Geological Oceanography Division, National Institute of Oceanography, Dona, Paula-403 004) : Changing depositional environments during the late quaternary along the western continental margin of India. J Indian Ass Sedimentologists 1998, 17(2), 147-56.

Sedimentological and palaeoceanographic studies were carried out on two sediment cores collected within the Oxygen Minimum Zone (OMZ-between 150 to 1200 m water depth) along the western continental margin of India. The glacial to interglacial variations on a shallow core of Cochin, suggests that the average sedimentation rates were very high <126>-13.2 cm/kyr) and varied widely during the Holecene and the late Pleistocene. Grain size measurments reveal that the clay content varied with the Late Quaternary climatic changes, as inferred from the stable isotope studies. The boundary between the Stage 2 and 1 is marked by a pronounced increase in the flux of terrigenous clays and a fall in organic carbon (COrg and carbonate (CaCO3) content. The rapid sea level fluctuations during the deglaciation and the proximity of the core site to the continent during the lowered sea level, lead to a relatively high average sedimentation rate. Contrastingly, a core from the isolated topographic high off Goa showed relatively lower average sedimentation rates (<126>5.2 cm/kyr) during the Holocene and the late Pleistocene. The contrasting sedimentation features observed at two different locations within the same oceanographic regime underlines the fact that topographic features and proximity of the core site to the continent controls the sedimentation rates during the late Quaternary.

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012886   Tewari R C (Department of Geology, D.S. College, Aligarh-202 001) : Framework mineralogy and provenance of early permian Gondwana rocks of Giridih and adjoining basins, Eastern India. Indian J Petrol Geol 1998, 7(2), 71-84.

Early Permian Gondwana (Talchir, Karharbari and Barakar) sandstones of Giridih and adjoining basins of eastern India are immature to submature, lithic subarkosic and arkosic wackes and arenites. The wackes are abundant in Talchir, rare in overlying Karharbari and absent in the succeeding Barakar, whereas arenites occur in the Karharbari and Barakar. The textural and mineralogical characters of framework grains of quartz, feldspars, mica and rock fragments indicate their source largely from acid igneous rocks and low to medium grade metamorphic rocks and subordinate contribution from metasedimentary and basic rocks. Paleocurrent study locates the provenance conclusively towards south and southeast of the study area. The study confirms that the Early Permian Gondwana rocks of Giridih and adjoining basins of eastern India were derived mainly from granites, gneisses and schists of Chotanagpur paleohighlands to the south and southeast of the given basins.

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012885   Tatavarti R;Naryana A C;Manoj Kumar P;Shyam chand (Naval Physical and Oceanographic Laboratory, Defence R and D Organizat, , Thrikkakara, Cochin-682 021) : Mudbank regime of the Kerala coast during monsoon and non-monsoon seasons. Proc Indian Acad Sci-Earth Planet Sci 1999, 108(1), 57-68.

Field experiments conducted in the nearshore ocean to undedrstand the dynamics of mudbank of Kerala, south-west coast of India, are highlighted. Real time monitoring of the nearshore ocean of Purakkad, Kerala was accomplished using pressure transducers for nearshore surface wave measurements, and current sensors for nearshore velocity measurements. Comprehensive information on the spatial structure of mudbank was obtained from aerial surveys. Extensive data collected on surface waves and currents in the nearshore ocean, indicate that the infra-gravity (IG) waves (leaky modes and trapped edge wave modes), and far infra-gravity (FIG) waves coupled with strong shoreline reflections and undertow play an important role in the dynamics associated with the mudbanks of Kerala during the monsoon season. During the non-monsoon season evidence for progressive edge waves in the infragravity frequency band, an energetic gravity wave band and a strong undertow with weak reflections was observed.

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012884   Talapatra A K (NO, , 43/C Baikuntha Ghose Road, Calcutta-700 042) : Heavy mineral placer deposits of India with special reference to 3D-modelling in parts of offshore areas for resource evaluation : a suggestion. Indian J Geol 1999, 71(1-2), 105-15.

Heavy mineral deposits of India are mostly present as onshore placers along the well disposed long continuous beaches scattered throughout its east and west coasts. The offshore extension of these heavy mineral placer deposits have been established by systematic geoscientific surveys and detailed studies undertaken by the research vessels of the Marine Wing, Geoloical Survey of India along the coastal areas for placer mineral evaluation and prediction of offshore targets from known to unknown tracts. With this objective, an attempt has been made here to describe the nature of the sediments derived from the Indian subcontinent vis-a-vis the formation of heavy mineral placers to suggest an approach for resource modelling of these placer deposits; a test case from parts of east coast off Gopalpur, Orissa is described. It is suggested that use of 3D graphical presentation of offshore placer deposits from vibro core and grab sample data in combination with geostatistical techniques for proper estimation of the reserve of heavy munerals may be pursued. Such an approach is expected to be very useful for planning and designing of the exploitation programme for the offshore heavy mineral placer deposits of India after the proper assessment of their resource potential.

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012883   Subrahmanyam B (Geological Survey of India, , 1-2-99/3, St. 2, Habsiguda, Hyderabad-500 007) : Some results of trace element studies for kimberlites in Wajrakarur area, Andhra Pradesh. J appl Geochem 1999, 1(2), 111-4.

In Wajrakarur area, the spectral scanning of the heavy minerals from the pits (3m) put down over the electromagnetic conductor indication have been found to be useful in knowing the rocks of kimberlitic affinity under thick over burden. Based on these results, further probing at six probable locations for kimberlites has been recommended.

012882   Sridhar S G D;Mussain S M;Kumar V;Periakali P (Department of Applied Geology, University of Madras, Chennai-600 025) : Penthic ostracod responses to sediments in the Palk bay, off Rameswaram, southeast coast of India. J Indian Ass Sedimentologists 1998, 17(2), 187-95.

Calcium carbonate and organic matter content of each samples was correlated against the Ostracod population recovered in sediment samples from Palk Bay, off Rameswaram, southeast coast of India. It has been found that higher calcium carbonate and lower organic matter generally favour a higher population size. A correlation of the sand-silt-clay analysis with the observed Ostracod population shows that the siltysand and sand are more congenial substrates for the abundance of the fauna. The increase in population size in the intermediate segment of the transect than in the near shore and farther segments may be due to the occurrence of coral reefs. Based on SEM study, an attempt has also been made to observe the design of the surface, sculpture of Ostracod carapace in relation with the sediment.

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012881   Sreejith S;Mani R;Padmalal D (Environmental Sciences Division, Centre for Earth Science Studies, Thuruvikkal, P O Trivandrum-695 031) : Granulometric studies of the sediments of Sasthamcotta and Chelur lakes, Kerala : implications of hydrodynamic responses of lacustrine sediments. J Indian Ass Sedimentologists 1998, 17(2), 251-62.

Granulometric studies conducted in two fresh water lakes-the Sasthamcotta and Chelur lakes-of Kollam district, Kerala reveal drastic differences in the physical mechanisms to which the sediments are subjected during the transportational/depositional phases. The wind driven ripples that impinge on the lake banks selectively removes sediment particles either by saltation or by suspension and subsequently be deposted towards the inner-deeper (profundal) areas of the lakes. The profundal zones of both the lakes receive extremely fine, clay mineral rich particulates derived mainly from flocculation processes. Textural parametes and CM model also support the said sedimentation process.

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012880   Sreedhar Murthy Y (Centre of Exploration Geophysics, Osmania University, Hyderabad-500 007) : Images of the gravity field of India and their salient features. J Geol Soc India 1999, 54(3), 221-35.

During the last one decade or so, computers have revolutionised the practices in earth sciences the world over. Space technology provided the impetus and the necessary tools for presenting geoscientific data as images besides the usual coloured geological maps and geophysical contour presentations. The greatest advantage of an image is its enhanced visual perspective and its ability to bring out subtle features / trends that may be less discernible in ordinary contour maps. In India, geoscientists are yet to realise the full potential of image technology and to take advantage of it. The present article is a demonstration of the usefulness of geophysical images as a complement to their contoured versions. A rapid and cost effective method earlier devised by the author and his colleagues was adopted for digitising the Free-air, Bouguer and Isostatic gravity anomaly maps of India. The digital data thus produced were used for generating images in shaded relief and colour. These images reveal a number of interesting geological and tectonic features which have been highlighted. While some of these correspond to those already known, the others are distinguishable primarily in the images and therefore not reported.

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012879   Singh M;Singh R (NO, Y S Parmar University of Horticulture and Forestry, Nauni (Solan)-173 230) : Rainfall pattern of midhills of Solan in Himachal Pradesh. Indian J agric Res 1999, 33(3), 153-8.

Meteorological data of the Nauni, Solan observatory available from 1971 to 1995 was analysed and processed. The analysis shows that the annual rainfall was 1 15.6 mm. The highest rainfall was 4241.2 mm. in the year 1982, whereas the lowest rainfall was 529.5 mm in the year of 1984. The maximum rainfall received in the South-West monsoon season which was around 67 per cent of the total annual rainfall at the station. August was the wettest month and the November was the driest. The month of April was most variable and uncertainly of rainfall whereas, the August was least variable from rainfall. There is no Standard week which remained completely dry from 1971 to 1995.

012878   Shenoy N;Lokesh K N (Dept of Geology, Manipal Institute of Technology, Manipal-576 119) : Quality of groundwater of borewells in M.I.T. Campus, Manipal, Karnataka. Indian J envir Hlth 1999, 41(2), 144-8.

From the analysis of 15 groundwater samples collected from the bore wells of Manipal Institute of Technology Campus, Manipal, it is found that the physicochemical parameters are within the maximum permissible limits of drinking water standards. However, low fluoride (<60>0.6 mg/L) is observed in all the groundwater samples and high iron (<60> 1.0 mg/L) in one of the samples. The study also reveals that groundwater of this campus is dominated by bicarbonate anion with magnesium and calcium cations.

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012877   Sharma R S (Department of Geology, Banaras Hindu University, Varanasi-221 005) : Crustal development in Rajasthan craton. Indian J Geol 1999, 71(1-2), 65-80.

Granulites are mainly metapelitic and metabasic, intruded by norite, followed by 1.72 Ga old charnockite-granodiorite, whose thermal overprinting is seen in the development of andalusite and hornfelsic texture. The pelitic granulites, like the BGC schists, record a polymetamorphic assemblage, in which crystallization of the Al-silicate phases is in the order : kyanite--<62> sillimanite--<62> kyanite (needle), with andalusite as the last phase. The basic granulite is characterized by corona of garnet-diopside-quartz at the contact of the once stable hypersthene-plagioclase pair. The P-T estimates (850°-650°C; 10-7 kbar) in the pelitic and basic granulites reveal an anticlockwise P-T path favouring magmatic underplating model for continental crustal thickening during evolution of the Delhi fold belt. This is supported by recent deep seismic reflection studies, which show a dome-shaped reflector below the Delhi belt and a high gravity over it. There is ample evidence to suggest that the Aravalli belt evolved through ensialic orogenesis prior to the Delhi belt. In this event, crustal thickening was by structural duplication during basinal deformation. This caused rupture of the lithosphere, whose A-subduction was westward, as inferred from heat flow and thermal gradient. By decoupling of the upper mantle, hot asthenosphere material rose and underplated the overlying crust in the region. The crust was thus softened, even partially melted, and depressed to form an elongated ensialic basin for the Delhi sedimentation. With continued compression, the Delhi as well as the already deformed Aravalli and BGC rocks were recrystallized and uplifted to build the Aravali mountain belt. The compression at depth was terminated by shearing which helped exhumation of the granulites, now seen as elliptical outcrops amidst the BGC and also as `fragments' within the Delhi metamorphics. In the deep seismic reflection profiles, this shear zone is seen as a strong reflector rising fron near the Moho with its surface outcrop coinciding with the NE-SW trending shear zone in the region. The crustal development in Rajasthan during Proterozoic is, thus, related to the Aravalli mountain building phenomenon, which may be cited as a classic example of a sequence of crustal thickening by magmatic underplating following collision.

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012876   Sharma R K;Pandit M K;Warrier S (NO, Geological Survey of India (WR), Jhalana Dungari, Jaipur-302 017) : Hybrid acid xenoliths in dolerite dykes intruding deccan flood basalts, Pune-Ahmednagar region, Western India. J Geol Soc India 1999, 54(3), 303-8 .

Deccan flood basalt in Pune - Ahmednagar region, western India, is intruded by NE-SW, NW-SE and E-W trending dolerite dyke swarms, post-dating the main eruptive phase. The NE-SW trending dykes host a number of large (~1 to <62> 5 m across) ellipsoidal rhyolitic and granitic xenoliths that show effects of hybridization along their rims. Granitic xenoliths contain fractured and partially assimilated crystals, whereas in the fine-grained rhyolites hybridization is manifested in the development of flow structures and chlorophaeite-filled amygdules. Hybridization of the xenoliths has resulted in wide variation in silica abundance, whereas the REE patterns show remarkable similarity. This indicates that hybridization was limited only to the readjustment of relatively mobile elements, resulting in alkali exchange across the interface. The rhyolitic xenoliths might have resulted from the fusion of the crust by basic magma, while the granitic xenoliths possibly represent the basement component. Incomplete assimilation of xenoliths by the melt as evidenced by limited reaction, further corroborates the incorporation of xenoliths at a shallow level, when the uprising basic melt had considerably fractionated and cooled. The fractionated nature of host dolerite dyke is also confirmed by moderate MgO, high FeO¹ and LREE enrichment.

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012875   Shahid S;Nath S K;Patra H P (Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur-721 302) : Integrated approach for groundwater investigation around Nazarganj near Kasai river bed, Midnapur dist. West Bengal. J appl Hydrol 1999, 12(4), 15-21.

Combined geological, geophysical and hydrogeological investigation around Nazarganj (ht. 22°23°30°N, long 87°19%E) near Kasai river, Midnapur Dist. West Bengal is used to study the ground water potential of the area. Geological and geomorphological studies from satellite imagery, reveal the existence of river terraces. Geoelectric sounding results verified from borehole data indicate the presence of a shallow uncomfined aquifer. A thick deposit of sand bed, as predicted from geomorphological and geophysical studies, is also confirmed from borehole data. Pumping test data show an average yield of about 35,000 liters/hour at an approximate drawdown of 0.18 meter for a continuous pumping of 24 hours. The grain size analysis shows that the porosity of aquifer varies between 30% and 40%. The potability of water in the area is established through chemical analysis of water sample collected from the pumping well.

012874   Sengupta R;Bhattacharyya S;Bhattacharyya J; Rakshit S;Majumdar S;Deb Ray D K;Gupta S;Raghav S (NO, Geological Survey of India, Marine Wing, 9 & 10/1 Raja S C Mallick Road, Calcutta-700 032) : Sediment distribution and heavy mineral potential of the shoreface zone of southern Orissa between Sonapurapeta and Chatrapur. J Indian Ass Sedimentologists 1998, 17(2), 231-7.

Dynamic zone of the sea floor between 0 and 10 m water depths was negotiated off the coastal stretch of 26 km between Behuda river confluence and Chatrapur in southern Orissa. The survey carried out on 14 lines transverse to the shore at 2 km interval reveals a smooth seafloor with gentle slope having gradient 1 : 80 increasing to 1 : 30 off Markandi river and Kharl nala at 2 to 4 m isobaths. The 0 to 10 m shoreface extends upto a distance of 700-800 m. The seafloor is essentially occupied by very fine and fine sand. Medium sand generally well sorted occurs as isolated patches and at 5 to 6 m water depths off Ramayapatnam and Gopalpur, possibly representing a part of the relict sediment. Scatter plots of different statistical parameters indicate deposition by wave action in a beach environment. The seabed sediments are quite enriched in heavy minerals (ilmenite, sillimanite, garnet, monazite, zircon, rutile etc.) with maximum incidence being 49 wt percent having average value of 14 wt percent for 78 samples. The seabed between 2 and 4 m isobaths stands out as the most prolific zone in respect of heavy mineral potential (10 to 20 wt percent) in fine to very fine sand. The sediment characteristics and its heavy mineral content suggest that these are the remnants of a huge sand mass rich in heavy minerals, which migrated towards the shore under the influence of the transgressive sea during the Holocene.

012873   Sen N (NO, , 127 C, Rashbehari Avenue, Calcutta-700 019) : Seismogenic fault at Latur. Indian J Earth Sci 1997, 24(3-4), 36-44.

One hundred kilometre long volcanogenic greenstone bed of eastern Dharwars outcrops between the southeastern Deccan traps and the adjacent Bhimas in the northwest and the Cuddapahs to the southeast. It strikes NW-SE and aligns with the NW-SE trending seismogenic fault at Latur. It is suggested that this bed extends below the traps and instability along this bed caused the damaging M 6.3 earthquake on 30 September, 1993 at Latur. Recent geophysical studies have indicated the presence of a basic body within the Peninsular Gneiss below the 350-400 m thick traps. Based on the structure contour on the plane of the seismogenic fault and other data, it is inferred that the earthquake probably began as a new bedding plane fault, at 6 km depth, close to the basal contact of the greenstone with the Peninsular Gneiss, and later disturbed other parts of the bed near the root. Available data indicate that the majority of earthquakes in the stable continental region of Dharwar craton occurred to close proximity of the volcanogenic greenstones of eastern Dharwars. There were hardly any earthquakes in western Dharwars, which are generally bereft of volcanogenic greenstones. This preference for incompetent beds like greenstones appear to offer a clue in understanding SCR earthquakes in the Archeans of S. India.

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012872   Saxena RM;Nandi B (NO, , ) : Western disturbances : role of upper tropospheric features in their development. Vatavaran 1998, 22(2), 1-8.

An attempt has been made to dispel some myths about WDs. Also, the role of upper tropospheric features is emphasised in intensification/weakening of WDs. Careful analysis is necessary to locate the position of trough in westerlies and wind maxima should be precisely ascertained by isotach analysis, to locate sector of favourable upper level divergence. Once the synoptic features are identified, they should be coupled with local parameters along with the satellite imageries to provide complete weather perspective. This integrated approach has been used to develop a check list for forecasting Rain/Thunder Showers in association with WDs. Three such check lists have been developed for Chandigarh, Bareilly & Bagdogra based on author's personal experience.

012871   Saxena R M;Ravi N;Singh VC;Prabhakara K;Misra S (NO, , ) : Satellite study on western disturbances over northwest India during the winter months. Vatavaran 1998, 22(2), 34-7.

Comprehensive study of Western Disturbances (WDs) over northwest India during winter months (November to February) has been carried out with respect to the type of cloud mass observed in the satellite cloud imageries. It is found that the Vortex and the Overcast type of cloud patterns associated with the WDs result in fairly-widespread to widespread rainfall over northwest India.

012870   Sankaran A V (NO, , 10, P and T Colony, 1 Cross, II Block, R T Nagar, Bangalore-560 032) : Diamonds in komatiites and some contemporary views about this gem-carbon. Curr Sci 1999, 77(12), 1574-7.

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012869   Sankar Kumar Nath;Shahid D (Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur-721 302) : Joint application of seismic refraction and vertical electrical sounding for the delineation of shallow aquifers. Curr Sci 1999, 77(12), 1612-23.

Inversion of seismic refraction and vertical electrical sounding data alone may lead to incorrect parameter estimation in complex geological set-up, namely, blind zone in seimics, suppression and equivalence in geoelectrics. A unique solution may be achieved by integrating physically different sets of data into a joint or sequential inversion scheme. It has been introduced one such algorithm, wherein the seismic velocity-depth section from ray inversion guides the evolution of a well-resolved geoelectric section in 2D environment from 1D DC resistivity inversion by evolutionary programming. The synthetic models suffering from the suppression and equivalence problems could be successfully reconstructed using this approach. Three test sites at Keshpal, Tata Metalik and Salboni in Midnapur District, West Bengal were selected through remote sensing and GIS tools. By sequentially interpreting the seismic and resistivity data, could delineate a shallow aquifer with an average thickness of 6.8 m at Tata Metalik. At Salboni, however, a thin aquifer at 46 m depth needed an additional electrolog/litholog depth control for its delineation by the proposed joint approach.

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012868   Sahu B K (Department of Earth Sciences, IIT, Mumbai-400 076) : Advanced techniques for modelling porous and fractured rocks. SGAT Bull 1999, 1(2), 57-63.

Some of the important advanced modelling technologies that are currently used for porous media research. These new techniques yield very accurate and precise as well as realistic values for different types of porous media including unconsolidated sediments and soils, sedimentary rocks, fractured rocks as well as artificial materials such as packed beds, filters, polymers etc. Therefore, these techniques should replace the classical and continuum modelling approaches. The most important applications are in the field of oil and gas production, secondary and tertiary recovery of oil from reservoirs, ground water flow and dispersion, contaminant remediation etc. A key concept interlinking microscopic and megascopic behavior and vice verse is the new technology of percolation theory applied to disordered porous media instead of the false comfort under classical assumptions of homogeneity, ordered structures and continuum approximations. Basic concepts and applications of these new technologies for porous media respresentations are included.

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012867   Saha A K;Chakrabarti C;De S (Centre for Study of Man and Environment, , CK-11, Sector-2, Salt Lake City, Calcutta-700 091) : Genesis of arsenic in groundwater in parts of West Bengal. Indian J Earth Sci 1997, 24(3-4), 1-5.

Arsenic content of ground water at same depth within the same zone varies between wide limits. But it is interesting to note that no water sample from ponds or dug wells (i.e. within 15m depth) in the arseniours groundwater areas has been found to contain more than 0.01 mg/l arsenic. Within the arsenious areas, maximum arsenic content occurs in groundwater in the 20-60m range from <60>0.01 mg/l upto maximum of 3.0 mg/l. On the other hand, tube wells tapping the aquifer below 60m give practically arsenic-free water except in some wells in the Raninagar Block in Murshidabad where groundwater gives <62> 0.05 mg/l of arsenic. A general positive correlation between arsenic and iron contents in the South Bengal groundwater was noted by earlier workers from CGWB. However, the raw arsenic values (n=111) obtained in the course of the present study show a low positive correlation (+ 0.19) with Fe; correlation of arsenic with chloride, sulphate and hardness are also low. But when the arsenic values are log-transformed (i.e. log₁₀. As 10³) some of the correlations do improve. [Sediment samples from undisturbed core drillings were also analysed for arsenic and some other heavy metals. Significantly high correlation coefficient matrices between arsenic and the associated heavy metals (Pb, Cu, Fe and Mn) in borehole sediments are particularly important.]

012866   Roy M;Dhana Raju R (Atomic Minerals Directorate for Exploration and Research, Department o, , New Delhi-110 066) : Mineragraphy and electron microprobe study of the U-phases and pyrite of the dolostone-hosted uranium deposit at Tummalapalle, Cuddapah Dist., Andhra Pradesh and its implication on genesis and exploitation. J appl Geochem 1999, (NULL), 53-75.

Mineralogical characterisation, based on mineragraphy and electron microprobe (EMP) studies, has been attempted on the large tonnage, low-grade (ca.av. 0.045% U₃O₈), unusual dolostone-hosted uranium deposits at Tummalapalle, Rachakuntapalle and Gadankipalle, Cuddapah dist., Andhra Pradesh. These deposits extend over a distance of 140 km from Reddipalle in the west to Maddimadugu in the east. The mineralised dolostone is sandwiched between a lower massive dolostone and upper shale and cherty dolostone. It is stromatolite-bearing with impurities of phosphate and silicate detritus. Uranium mineralisation occurs along the bedding plane, carbonate-phosphate contact, micro-stylolites, grain boundaries of clasts and within pelloids, mainly in the form of ultrafine pitchblende (0.003 to 0.06 mm) in intimate association with pyrite (mainly biogenic variety) and disseminations in collophane-rich parts, besides as minor phases of coffinite, U-Si-Ti complex, U-Si complex and uranophane as well as a little in the adsorbed form with collophane. The associated ore minerals include mostly pyrite, molybdenite, chalcopyrite, bornite, digenite and covellite. EMP analysis carried out on the radioactive phases and associated pyrite of the dolostone hosted U mineralisation has indicated that: microscopically identified U-Ti complex is actually U-Si-Ti complex, since it contains appreciable amount of SiO₂ (17.49%); the major uranium phases like pitchblende, coffinite and U-Si-Ti complex are of low temperature formation due to their very little to almost nil contents of Th and analysed REE; V₂O₅ content is many orders more in these U-phases as compared to that of pyrite, and probably accounts for most of the V content (200-300 ppm) of host dolostone; and Arsenic content is the highest (1.86%) in diagenetic pyrite, and in biogenic pyrite, pitchblende and coffinite too it is in notable contents of about 0.3%. Since As bearing minerals, in general, and pyrite, in particular, are potential hosts for Au, recovery of Au and Ag apart from As, and V from U-phases as possible by-products is a distinct possibility during mineral processing of the U-ore under study. In such a scenario, the high cost of exploitation of recovering the U-ore due to its low grade of Ca 0.045% U₃O₈ can be compensated to a certain extent due to recovery of these precious and high value metals. Assuming a closed system, the average chemical ages, calculated from U, Th and Pb contents, of U-Si-Ti complex, pitchblende, coffinite and U-Si complex are respectively 698, 418, 24 and 223 Ma, which implies more than one episode of U-mineralisation in this deposit.

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012865   Roy F;Nair G J;Basu T K;Sikka S K;Kakodkar A; Chidambaram R;Bhattacharya S N;Ramamurthy V S (Seismology Division, Bhabha Atomic Research Centre, Mumbai-400 085) : Indian explosions of 11 May 1998 : Analysis of regional Lg and Rayleigh waves. Curr Sci 1999, 77(12), 1669-73.

Analysis of regional Lg and Rayleigh wave data pertaining to the Indian explosions of 11 May 1998 (POK2) has been presented. Strong Lg and Rayleigh waves have been recorded at several incountry stations. A comparison of Lg waves at Gauribidanur array (GBA), India corresponding to POK2 and that of the Indian explosion of May 1974 (POK1) shows an amplitude ratio of 3.7 between these events. This leads to a yield ratio of 4.83 between two events. Analysis of Rayleigh waves revealed that Nuttli's relation for estimation of surface wave magnitude (Ms) in the period range 3.0-12.0s based on eastern North American data is also applicable for the Indian region. The average M>V>s value of POK2 from regional data is obtained as 3.56. The yield estimate of POK2 as obtained from the regional data analysis is found consistent with earlier findings and the post shot radiochemical measurements.

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012864   Reddy P R;Venkateswarlu N;Koteswara Rao P; Prasad A S S S R S (NO, National Geophysical Research Institute, Hyderabad-500 007) : Crustal structure of peninsular shield, India from DSS studies. Curr Sci 1999, 77(12), 1606-11.

Moho boundary is deep (44 km) in the north-western part of the country especially in the region of Aravalli Fold Belt. Similarly, except for the coastal regions, the crust is also thick in the southern parts of the Peninsular Shield (37-45 km). The crust seems to become thinner (24 km) towards the northern parts of the west coast. Compared to the west, the crust towards the east coast seems to be either normal or thicker except for the prominent doming-up at the eastern flank of the West Bengal basin. However, it is relevant to state that absence of deep crustal information of the southern parts of the east and west coasts restricts the above statement to the region north of 15°N latitude. The average crustal thickness in the Dharwar Craton is 35 km, whereas the crustal thickness in the Proterozoic Cuddapah basin is about 40-43 km, with the maximum at its eastern margin. The large thickness of the tertiary sediments in the Cambay Basin and relatively thin crust in the region suggest further rifting also characterized by an upwarp in the Moho during the Late Cretaceous period, probably representing a transitional of the crustal structure in terms of geological and geochronogical setting and the inferred crustal composition, deep depressions in this prominent boundary associated with faults/fracture zones are presented along with the variations in the velocity structure;....

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012863   Rathore S S;Prabhu B N;Vijan A R;Vig K C; Misra K N (NO, KDM Institute of Petroleum Exploration, Oil and Natural Gas Corporatio, Dehradun-248 195) : K-Ar age of Ukra glauconites from the Kutch Basin, India. Proc Indian Acad Sci-Earth Planet Sci 1999, 108(1), 49-55.

Reports the K-Ar ages determined on glauconitic samples collected from the Ukra Member of the Mesozoic Bhuj Formation in two different sections, one located on the Ghuneri-Ghaduli road near Katesar Mahadeo temple and the other at the base of the Ukra hill in the northwestern part of the Kutch Mainland area. Three glauconite samples viz., Ukra_KT-1, Ukra_KT-4 and Ukra_{UH-3 have yielded K-Ar ages of 107.9±3.4 Ma, 105.5±3.3 Ma and 103.5±3.4 Ma, respectively. The sample UkraKT-1 treated with 0.5N HCl and analysed in duplicate has yielded a mean age of 104±2.3 Ma while the sample UkraKT-4 treated with 0.1N HCl has given an age of 106.5±3.3 Ma. The ages of the treated and untreated glauconites are indistinguishable within 2σ uncertainty with a mean of 105.2±1.3 Ma, which has been interpreted as the depositional age of the Ukra Member of the Mesozoic Bhuj Formation. The study has further indicated that mild acid treatment (up to 0.5N HCl) does not lead to any loss of radiogenic argon in the glauconites and can be helpful in purification of the samples.}

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012862   Rao L A K;Asif M;Rehan Ali S (Geology Department, Aligarh Muslim University, Aligarh) : Quantitative hydrogeomorphic investigation of Kali-Singh sub-basin within Rajgarh district, Madhya Pradesh, India. Indian J Earth Sci 1997, 24(3-4), 45-50.

Drainage patterns of the Kali-Sindh river sub-basin covering approximately 127 sq km within Rajgarh district, M.P. are identified/interpreted from aerial photographs. Quantitative analysis in terms of linear, areal and relief aspects are carried out. Bifurcation ratios are found well within the range of normal basin in which geological structures are observed. Values of the relief ratio and ruggedness number indicate more intense erosion on the slopes of basin and more slope steepness respectively.

012861   Rao C R M;Reddi G S;Rao T A S (Chemical Division, Gelogical Survey of India, , Hyderabad-500 068) : Determination of precious metals in copper, lead, zinc ores and concentrates from Bihar and Rajasthan. J appl Geochem 1999, (NULL), 77-81.

Determination of precious metals were carried out by HCl/bromine acid extraction followed by tellurium coprecipitation and estimation by AAS for gold and Nickel sulphide preconcentration followed by tellurium coprecipitation and estimation by the inductively coupled plasma mass spectrometry (ICP-MS) for the platinum group elements (PGE). The samples chosen were copper concentrate from Surda Mines, Bihar and zinc and lead ores and concentrates from Rampura Agucha Mines, Rajasthan as these belts have the potential for detailed study of their precious metal content. The results obtained indicate that the ores and concentrates investigated in the present study show 40 to 1200 ng/g of gold. Of these the copper concentrate exhibits the highest value of 1200 ng/g. Considering the high value of gold obtained in the copper value concentrate there is good scope of extracting this element as a byproduct. The PGE contents of the samples studied in the present work show low level occurrences ranging from 10 to 280 ng/g of the individual elements; copper concentrate showing the highest palladium value of 280 ng/g and highest rhodium value of 100 ng/g. Zinc concentrate show highest ruthenium value of 160 ng/g. These low values may not be of much significance for PGE recovery from these ores and concentrates.

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012860   Rao A T;Srinivasa Rao K;Srinivas S (Department of Geology, Andhra University, Visakhapatnam-530 003) : Petrology of basic granulites from Maruturau near Anakapalle in the eastern Ghats Granulite belt. J Geol Soc India 1999, 54(3), 279-89.

Basic granulites frequently occur in garnetiferous quartzo-feldspathic gneisses and rarely in garnetiferous sillimanite gneisses, calc-silicate rocks and quartzites in the entire Eastern Ghats Granulite Belt (EGGB). Commonly these basic layers are parallel to the foliation and are occasionally boudinaged. These share a common tectonic and metamorphic history with those of the associated litho-units. There are also unusual basic granulite dykes which crosscut the foliation in quartzo-feldspathic gneisses, folded calc-silicate rocks and basic granulites at Maruturu near Anakapalle in the EGGB. The two generations of basic granulites are even grained with a polygonal annealed mosaic and characterised by the mineral assemblage: coexisting pyroxenes and plagioclase. The mineral composition data of coexisting pyroxenes indicate large scale equilibrium at granulite facies conditions. Both types of basic granulites have almost similar bulk composition and have tholeiitic affinity. The basic granulite dykes have low contents of REE with a smooth distribution pattern and a general decrease from LREE to HREE. The revival of basic magmatism during post D1 and D2 at Maruturu reveals that extensional set-up recurs in the EGGB. The basic granulites of Maruturu are correlated with Proterozoic metabasic dykes in East Antarctica and Western Australia.....

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012859   Ramesh H S;Mahendran B (Dept of Environmental Engineering, S.J. College of Engineering, Mysore-570 023) : Assessment of subsurface water quantity in Kalayarkoil Union of Tamil Nadu. Indian J envir Hlth 1999, 41(2), 135-43.

Kalayarkoil Union in Sivagangai District of Tamil Nadu is located at a distance of 35 km from the Bay of Bengal and use of subsurface water in the area is on increase in recent years due to increasing water demand for agricultural and drinking purposes. Considering its proximity to sea, a study on the subsurface water quantity has been carried out to ascertain the safe yield. The study reveals that the magnitude of annual rainfall and ground water potential show decreasing trends. The critical drawdown and net safe yield are determined. Relationship between monsoon rainfall and rise in static water level (SWL) are also established.

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012858   Raju K K;Raju A N;Sudheer A S (Department of Geology, S.V. University, Tirupati-517 502) : Red sanders (Pterocarpus santalinus) : a biogeochemical study from southeastern part of Andhra Pradesh. J Geol Soc India 1999, 54(3), 259-66.

Trace element analysis of red sanders tree species (Pterocarpus santalinus) and their associated soils from deciduous forests of Chittoor, Cuddapah and Nellore districts in the southeastern part of Andhra Pradesh has been studied. The study shows that the heartwood of Pterocarpus santalinus is capable of accumulating large amounts of Sr, Zn and Cu.

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012857   Rajeshwara Rao N;Khare N;Periakali P (Department of Applied Geoloy, University of Madras, Guindy College Campus, A.C. College Building, Chennai-600 025) : Glandulina spinata Cushman - a rare foraminiferal species from inner shelf sediments of Bay of Bengal, off Karikkattukuppam, near Chennai, Southeast Coast of India. J Geol Soc India 1999, 54(3), 309-13.

Studies on recent foraminifera from inner shelf sediments of the Bay of Bengal, off Karikkattukuppam, near Chennai (latitude 13°O4' N; longitude 80°17' E), revealed the presence of a rare foraminiferal species. Taxonomic observations reveal this spinose taxon to be Glandulina spinata Cushman and is reported herein for the first time from Indian waters. Available data suggest it to be a tropical, inner shelf dwelling taxon, with a preference for muddy substrate.

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012856   Rajagopalan V;Paul A K;Tripathi B K; Thirupathi P V;Dhana Raju R;Dipica M (Atomic Minerals Directorate for Exploration and Research, Department o, , Hyderabad-500 016) : Petroraphy and mineral chemistry of the U-Ti complex and anatase in radioactive granite mylonite from Mulapalle area, Cuddapah district, Andhra Pradesh, India. J appl Geochem 1999, 1(2), 89-98.

Mulapalle area, near Rayachoti in the south-western environs of the Cuddapah basin, exposes crystalline rocks comprising Peninsular gneiss in the low-lying area and a ridge of Lakkireddipalle grey and pink granitoids (Closepet equivalent ?) that are intruded by basic dykes and micro-granite. Numerous uranium anomalies were located in the fracture zones within the deformd Closepet-equivalent granitoid (cataclasite, mylonite and phyllonite). The fractures trending ENE-WSW, NNE-SSW and NW-SE acted as channel ways and structural traps for the uranium mineralisation and richer concentrations are located where there is intense activity of wall-rock alterations, viz., hematitisation, chloritisation and sericitisation. Petrographically, the radioactive drilled-core samples from boreholes, MUP-16 and 16A are essentially granite mylonites and phyllonites, with alternate folded bands of cryptocrystalline (cherty) silica and sericitic-chloritic matter, with opaque (suspected to be of a uranium phase) bands along micro-shears and altered crypto-crystalline qurtzo-feldspathic mass with smeared ferruginous material. Clusters and trails of alpha tracks on CN films exposed on the radioactive samples are of medium density with the locii of disseminated and vein type uranium mineralisation related to micro-structures. The U-phases (U-Ti complex, minor skeletal uraninite) are associated mainly with the oxide ore minerals of hematite, specular hematite, minor ilmenite, anatase and limonite, besides a few sulphides of pyrite and chalcopyrite. Mineral chemistry based on EMP analysis of uranium phases and associated accessory ore minerals reveal that U-Ti complex and anatase are the two distinct radioactive phases closely associated with hematite, with the former showing variable content of U, Th and total Fe, whereas in case of anatase and hematite there is no perceptible inter-and intra grain variation in composition....

012855   Rai S S;Singh S K;Rajagopal Sarma P V S S; Srinagesh D;Reddy K N S;Prakasam K S;Satyanarayana Y (NO, National Geophysical Research Institute, Uppal Road, Hyderabad-500 007) : What triggers Koyna region earthquakes - preliminary results from seismic tomography digital array. Proc Indian Acad Sci-Earth Planet Sci 1999, 108(1), 1-14.

Cause for prolific seismicity in the Koyna region is a geological enigma. Attempts have been made to link occurrence of these earthquakes with tectonic strain as well as the nearby reservoirs. With a view to providing reliable seismological database for studying the earth structure and the earthquake process in the Koyna region, a state of the art digital seismic network was deployed for twenty months during 1996-97. Reports the results from this experiment covering an area of 60x80 km² with twenty seismic stations. Hypocentral locations of more than 400 earthquakes confined to 11x25 km² reveal fragmentation in the seismicity pattern - a NE - SW segment has a dip towards NW at approximately 45°, whilst the other two segments show a near vertical trend. These seismic segments have a close linkage with the Western Ghat escarpment and the Warna fault. Ninety per cent of the seismicity is confined within the depth range of 3-10 km. The depth distribution of earthquakes delimits the seismogenic zone with its base at 10 km indicating a transition from an unstable to stable frictional sliding regime. The lack of shallow seismicity between 0 and 3 km indicates a mature fault system with well-developed gouge zones, which inhibit shallow earthquake nucleation. Local earthquake travel time inversion for P- and S- waves show ≈ 2% higher velocity in the seismogenic crust (0-10 km) beneath the epicentral tract relative to a lower velocity (2-3%) in the adjoining region.....

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012854   Periakali P;Padma S (Department of Applied Geology, University of Madras, Guindy Campus, Chennai-600 025) : Mercury in Pulicat lake sediments, east coast of India. J Indian Ass Sedimentologists 1998, 17(2), 239-44.

Higher concentration of mercury in the sediment samples from Pulicat lake during the post-monsoon period (av 9.85 μg/g) is due to the adsorption of mercury with organic matter. Low organic carbon and lack of fresh water, reduces the concentration of mercury in the sediments during pre-monsoon period (av 9.35 μg/g). The transportation of mercury and organic carbon is accomplished through heavy rainfall, high run-off and the supply of fresh water from the river Kalangi in the monsoon period.

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012853   Parthasarathy R;Surya Prakash Rao K;Das V K (Water Quality Monitoring Laboratory, R.W.S. Panchayat Raj Department, , Mahaboobnagar) : Comparative study of defluoridation techniques and their application in rural areas. J appl Geochem 1999, 1(2), 115-20.

Fluorosis, a crippling disease, is caused by intake of exacess fluoride mainly through drinking water. Various defluoridation methods of drinking water are developed by different scientists. The performance, merits and limitations of these defluoridation techniques, in the field have been studied and evaluated in this paper. On the basis of evaluation it is advisable to adopt scientific source finding to locate fluoride free water sources in rural areas before going in for de-fluoridation techniques.

012852   Nalawadi A R;Bhat M S;Chavadi V C (Department of Studies in Geology, Karnatak University, Dharwar-580 003) : Textural variations in the Kali river sediments, Uttara Kannada, Karnataka. J Indian Ass Sedimentologists 1998, 17(2), 167-76.

Analysis of sediments from Kali and its tributary shows mean grain size ranging from granule to fine sand class with majority being coarse sands. In general there is a decrease in grain size towards downstream, whereas, the tributary sediments vary in their mean size from very coarse to medium sand with majority of them being coarse. An attempts is made to study the textural variations of sediments along the Kali river channel affected by the regulated water discharge with that of the tributary sediments.

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012851   Nagamalleswara Rao B (Department of Geology, , Visakhapatnam-530 003) : Density, mineralogy and textural studies of the beach and dune placer deposits of Andhra Pradesh coast. J Indian Ass Sedimentologists 1998, 17(2), 157-65.

Density (p), composition and textural measurements were carried out on the Visakhapatnam-Bhimunipatnam (VB), Vishishta Godavari-Upputeru(VGU) and Hamsaladivi-Manginipudi (HM) beach and dune placers. The placers are of fine sand range, highest density in VB implicit rich in garnet, ilmenite, rutile, zircon, monazite; reflects coarser grain size and lowest in HM placers where magnetite, pyroxene minerals are abundant, characterised by fine grains. Well sorted sands indicate dominance of the ilmenite/magnetite mode. Heavy minerals increase with smaller grain size as sorting improves.

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012850   Nag S;Senupta S K;Gaur R K;Absar A (Geological Survey of India, , Lucknow-226 024) : Alkaline rocks of Samchampi-Samteran, district Karbi-Anglong, Assam, India. Proc Indian Acad Sci-Earth Planet Sci 1999, 108(1), 33-48.

Samchampi-Samteran alkaline igneous complex (SAC) is a near circular, plug-like body approximately 12 km² area and is emplaced into the Precambrian gneissic terrain of the Karbi Anglong district of Assam. The host rocks, which are exposed in immediate vicinity of the intrusion, comprise granite gneiss, migmatite, granodiorite, amphibolite, pegmatite and quartz veins. The SAC is composed of a wide variety of lithologies identified as syenitic fenite, magnetite ± perovskite ± apatite rock, alkali pyroxenite, ijolite-melterigite, carbonatite, nepheline syenite with leucocratic and mesocratic variants, phonolite, volcanic tuff, phosphatic rock and chert breccia. The magnetite ± perovskite ± apatite rock was generated as a cumulus phase owing to the partitioning of Ti, Fe at a shallow level magma chamber (not evolved DI = O1). The highly alkaline hydrous fluid activity indicated by the presence of strongly alkalic minerals in carbonatites and associated alkaline rocks suggests that the composition of original melt was more alkalic than those now found and represent a silica undersaturated ultramafic rock of carbonated olivine-poor nephelinite which splits with falling temperature into two immiscible fractions - one ultimately crystallises as alkali pyroxenite/ijolite and the other as carbonatite. The spatial distribution of varied lithotypes of SAC and their genetic relationships suggests that the silicate and carbonate melts, produced through liquid immiscibility, during ascent generated into an array of lithotypes and also reaction with the country rocks by alkali emanations produced fenitic aureoles (nephelinisation process).....

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012849   Mukherjee A;Rao K S;Babu E V S S K (NO, National Mineral Development Corporation Limited, Khanij Bhavan, Masab Tank, Hyderabad-500 028) : Chemistry of garnet and picro-ilmenite xenocrysts from kimberlites of Venkatampalli Pipe-7 (Anantapur district) and Kotakonda (Mahaboobnagar district) Andhra Psradesh: their significance in diamond exploration. J appl Geochem 1999, 1(2), 99-104.

Geothermometry and oxygen barometry of ilmenite-magnetite pairs of Venkatampalli kimberlite pipe-7 yielded a temperature of 1200°C and oxygen fugacity value of 10^-8.3 the values of log fO₂ and T fall in the equilibria field defined by iron-wustite (IW) and wustite-magnetite (WM). The Cr₂O₃ vs CaO plots of garnet categorise them as chrome rich, subcalcic "G10" garnets which are supposed to be cogenetic with diamonds and thus indicate that these are very much from the diamond stability field. The T and log fo₂ values of 1050°C and -10.3 for Kotakonda kimberlite body and absence of G10 garnets based on Q-cluster analysis of 31 garnet grains indicates its sampling from outside the diamond stability field. Hence, it is possible that Kotakonda kimberlite is non-diamondiferous.

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012848   Mishra B;Pal D C;Panigrahi M K (Department of Geology and Geophysics, Indian Institute of Technoloy, Kharagpur-721 302) : Fluid evolution in quartz vein-hosted tungsten mineralization in Chhendapathar, Bankura district, West Bengal: evidence from fluid inclusion study. Proc Indian Acad Sci-Earth Planet Sci 1999, 108(1), 23-31.

Tungsten mineralization in Chhendapathar area is hosted by quartz veins that traverse mostly the metasediments in and around Jikhu Nala. Fluid inclusion microthermometric experiments reveal the presence of four distinct types of inclusions. These are: aqueous biphase, monophase carbonic, aqueous carbonic and halite-bearing polyphase inclusions. Salinity-temperature variation points towards the presence of two fluids of contrasting salinities and both independently followed simple cooling paths without any indication of fluid mixing. The P-T of mineralization was calculated from the intersection of coexisting and coeval aqueous biphase, carbonic and halite-bearing inclusions. The deduced values range from 1.63 kb/361°C to 2.30 kb/385°C. However, the initial temperature must have been much higher as indicated from the high dissolution temperature (<62> 450°C) of halite. Transportation of tungsten in the high saline fluid was facilitated by cation-tungsten pairing, i.e., with the help of Na₂WO₄ and/or NaHWO₄ complexes. A rapid fall in solubility in such fluid with falling temperature (in the range of 300-400°C), and by occasional fluid-rock interaction triggered precipitation of wolframite.

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012847   Manivannan S;Shanthi R;Sundarraman S (Soil and Water Conservation Engg, ICAR Research Complex, Ela, Old Goa, Goa-403 402) : Applicability of soil conservation service runoff model for small tank catchments in southern Tamil Nadu. J appl Hydrol 1999, 12(4), 29-34.

Runoff model developed by Soil conservation Service, United State Department of Agriculture (SCS, USDA, 1964) has been tested for climatic conditions of Ramanathapuram district of Tamil Nadu in three selected tank catchments Viz. Puseri, Chinnakannakudi small and Maravaikudi. The predicted and observed runoff values were statistically analysed. The correlation coefficient between predicted and observed runoff values for Puseri, Chinnakannankudi small and Maravailkudi tank catchments are 0.996, 0.972 and 0.989 respectively. The Chi-square test showed that there was no significant variation between predicted and observed values at 5 per cent level. Therefore, the runoff model developed by SCS (1964) can be used at Southern Tamil Nadu with accuracy.