A stream sediment geochemical survey of the Ganga River headwaters in the Garhwal Himalaya

Abstract

This study models geochemical and adjunct geologic data to define provinces that are favorable for radioactive-mineral exploration. A multi-element bed-sediment geochemical survey of streams was carried out in the headwaters region of the Ganga River in northern India. Overall median values for uranium and thorium (3.6 and 13.8 ppm; maxima of 4.8 and 19.0 ppm and minima of 3.1 and 12.3 ppm respectively) exceed average upper crustal abundances (2.8 and 10.7 ppm) for these radioactive elements. Anomalously high values reach up to 8.3 and 30.1 ppm in thrust zone rocks, and 11.4 and 22.5 ppm in porphyroids. At their maxima, these abundances are nearly four-and three-fold (respectively) enriched in comparison to average crustal abundances for these rock types. Deformed, metamorphosed and sheared rocks are characteristic of the main central thrust zone (MCTZ). These intensively mylonitized rocks override and juxtapose porphyritic (PH) and proterozoic metasedimentary rock sequences (PMS) to the south. Granitoid rocks, the major protoliths for mylonites, as well as metamorphosed rocks in the MCT zone are naturally enriched in radioelements; high values associated with sheared and mylonitized zones are coincident with reports of radioelement mineralization and with anomalous radon concentrations in soils. The radioelement abundance as well as REE abundance shows a northward enrichment trend consistent with increasing grade of metamorphism indicating deformation-induced remobilization of these elements. U and Th illustrate good correlation with REEs but not with Zr. This implies that zircon is not a principal carrier of U and Th within the granitoid-dominant thrust zone and that other radioelement-rich secondary minerals are present in considerable amounts. Thus, the relatively flat, less fractionated, HREE trend is also not entirely controlled by zircon. The spatial correlation of geologic boundary zones (faults, sheared zones) with geochemical and with geophysical (Rn) anomalies infers ore mineralization by hydrothermal processes generated during multiple episodes of deformation and thrusting. The geologic setting of the anomalies also suggests that crystalline rocks (MCT Zone) along the nearly 2500 km length of the LesserHimalayan belt, where in the vicinity of thrust and fault zones, have potential for radioelement mineralization. Zones of higher concentrations of radioelements delineated by this study and locations of anomalous radon discharge determined by other investigations may indicate a potential health hazard over the long term. However, the low human population density precludes direct manifestation of health effects attributable to chronic exposure to these radioelements; however, the magnitude of natural concentrations suggests the need for more detailed studies and monitoring.

Geochemistry and provenance of bed sediments of the large rivers in the Tibetan Plateau and Himalayan region

“…Element geochemistry plays an important role in the studies of paleoenvironment, paleoclimate changes, and provenance tracing, and Nd isotope is supposed to be a good provenance tool, as it is very poorly influenced during the processes of weathering, transport, and diagenesis (e.g., Nesbitt 1979;Fleet 1984;Goldstein et al 1984; Goldstein and Jacobsen 1988;Taylor and McLennan 1985;McLennan 1989;Revel et al 1996;Najman 2006). In recent years, major and trace elements and Sr-Nd isotopic tracing of sediments have been widely used in riverine geochemical researches in the Tibetan Plateau-Himalayan orogen, and these studies have mainly focused on the middle and lower reaches of rivers (e.g., Ahmad et al 1998;Dekov et al 1998;Zhang et al 1998;Gaillardet et al 1999;Yang and Li 1999;Galy and FranceLanord 2001;Clift and Blusztajn 2005;Clift et al 2002;Singh and France-Lanord 2002;Yang et al 2002aYang et al , b, 2004Yang et al , 2007Lee et al 2003;Dalai et al 2004;Garzanti et al 2005Garzanti et al , 2010Chappell et al 2006;Mukherjee et al 2007;Borges et al 2008;Singh et al 2008;Li et al 2009;Rahaman et al 2009;Galy et al 2010;Hoang et al 2010;Singh 2010;Alizai et al 2011).…”

Distribution patterns of salinity and <sup>222</sup>Rn in Yatsushiro Inland Sea, Kyushu, Japan

“…There are many rivers in the world with high 222 Rn concentration discharging to coastal areas (Al-Masri and Blackburn 1999, Cook et al 2003, Giap 2003, Marques et al 2004, Mukherjee et al 2007, Pourhabib et al 2011. In order to exclude the effect of high radon concentration rivers on the Dulaiova et al (2005) approach for measuring SGD, EC time series were merged with radon concentrations monitored to locate SGD signals along the coast line of the Yatsushiro Sea, Kyushu Island, southwest Japan.…”

Thorium and Total REE Correlation in Stream Sediment Samples from Lingga Regency

“…The use of stream sediment geochemical survey in the search for mineral deposits is based on the premise; those sediments contain elements that are mobilized by weathering from adjacent watersheds into streambeds. Consequently, the chemistry of the sediments is a representative of the drainage basin composition [5,6].…”

“…Although REE comprise significant amounts of many minerals, almost all production came from less than 10 minerals, Eksplorium p-ISSN 0854-1418 Volume 39 No. 1, Mei 2018: [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] e-ISSN 2503-426X 3 such as apatite, bastnasite, monazite, xenotime, gadolinite, and cerianite. Those minerals are described with different elemental formulas, which are mobilized by weathering from adjacent watersheds into streambeds and affect the chemical content.…”

“…Instead of be considered as a sink for trace metals, stream sediments can act as source of metals depending on the change of the environmental condition [1][2][3][4][5]. The contaminations sources can be estimated from stream sediment analysis, which usually not detected on water monitoring [1].…”