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E. A. Petrov 《Doklady Earth Sciences》2007,412(1):141-143
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Gamma activity from the naturally occurring radionuclides namely, 226Ra, 232Th, the primordial radionuclide 40K was measured in the soil of Cuihua Mountain National Geological Park, China using γ-ray spectrometry technique. The mean
activity of 226Ra, 232Th and 40K were found to be 27.2 ± 6.5, 43.9 ± 6.2 and 653.1 ± 127.6 Bq kg−1, respectively. The concentrations of these radionuclides were compared with the typical world values and the average activities
of Chinese soil. The radium equivalent activity, the air absorbed dose rate, the annual effective dose rate, and the external
hazard index were evaluated and compared with the internationally approved values. All the soil samples have Raeq lower than the limit of 370 Bq kg−1 and H
ex less than unity. The overall mean outdoor terrestrial gamma dose rate is 66.3 nGy h−1 and the corresponding outdoor annual effective dose is 0.081 mSv. 相似文献
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Stacey C. Priestley Daniel L. Wohling Mark N. Keppel Vincent E. A. Post Andrew J. Love Paul Shand Lina Tyroller Rolf Kipfer 《Hydrogeology Journal》2017,25(7):2031-2047
The investigation of regionally extensive groundwater systems in remote areas is hindered by a shortage of data due to a sparse observation network, which limits our understanding of the hydrogeological processes in arid regions. The study used a multidisciplinary approach to determine hydraulic connectivity between the Great Artesian Basin (GAB) and the underlying Arckaringa Basin in the desert region of Central Australia. In order to manage the impacts of groundwater abstraction from the Arckaringa Basin, it is vital to understand its connectivity with the GAB (upper aquifer), as the latter supports local pastoral stations and groundwater-dependent springs with unique endemic flora and fauna. The study is based on the collation of available geological information, a detailed analysis of hydraulic data, and data on environmental tracers. Enhanced inter-aquifer leakage in the centre of the study area was identified, as well as recharge to the GAB from ephemeral rivers and waterholes. Throughout the rest of the study area, inter-aquifer leakage is likely controlled by diffuse inter-aquifer leakage, but the coarse spatial resolution means that the presence of additional enhanced inter-aquifer leakage sites cannot be excluded. This study makes the case that a multi-tracer approach along with groundwater hydraulics and geology provides a tool-set to investigate enhanced inter-aquifer leakage even in a groundwater basin with a paucity of data. A particular problem encountered in this study was the ambiguous interpretation of different age tracers, which is attributed to diffusive transport across flow paths caused by low recharge rates. 相似文献
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R. Bagheri S. Mehregan A. Yousefi E. Mirrezaei 《International Journal of Environmental Science and Technology》2017,14(11):2443-2450
In this work, accumulation of cosmogenic radionuclide 7Be in seven species of lichens was determined using HPGe detectors in autumn season. Ramsar city which is located in the north of Iran as one of the high-level natural radiation areas in the world was considered. Lichen species represented good potential in accumulation of 7Be radionuclide. The foliose species of Xanthoria parietina with the highest activity concentration value of 112.8 ± 1.8 Bq kg?1 was introduced as bioindicator for accumulation of 7Be radionuclide. Cladonia rangiformis species has got minimum concentration of 64.5 ± 0.8 Bq kg?1. Also from thallus morphology viewpoint, results showed that 7Be accumulation in foliose species is higher than in fruticose and crustose lichens species. Also there was relatively large positive correlation between 7Be and 226Ra activity concentrations in lichens species. 相似文献
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U-Pb systems were examined in samples (ranging from 4 to 10 cm3 in volume) of ore material taken from along a 3.5-m profile across a zone of U mineralization exposed in an underground mine at the Strel’tsovskoe U deposit in eastern Transbaikalia. The behaviors of two isotopic U-Pb systems (238U-206Pb and 235U-207Pb) are principally different in all samples from our profile. While the individual samples are characterized by a vast scatter of their T(206Pb/238U) age values (from 112 to 717 Ma), the corresponding T(207Pb/235U) values vary much less significantly (from 127 to 142 Ma) and are generally close to the true age of the U mineralization. The main reason for the distortion of the U-Pb system is the long-lasting (for tens of million years) migration of intermediate decay products in the 238U-206Pb(RD238U) in the samples. This process resulted in the loss of RD238U from domains with high U concentrations and the subsequent accommodation of RD238U at sites with low U concentrations. The long-term effect of these opposite processes resulted in a deficit or excess of 206Pb as the final product of 238U decay. The loss or migration of RD238U are explained by the occurrence of pitchblende in association with U oxides that have higher Si and OH concentrations than those in the pitchblende and a higher +6U/+4U ratio. The finely dispersed character of the mineralization and the loose or metamict texture of the material are the principal prerequisites for RD238U loss and an excess of 206Pb in adjacent domains with low U concentrations. Domains with low U contents in the zone with U mineralization serve as geochemical barriers (because of sulfides contained in them) at which long-lived RD238U(226Ra, 210Po, 210Bi, and 210Pb) were accommodated and subsequently caused an excess of 206Pb. The 235U-207Pb system remained closed because of the much briefer lifetime of the 235U decay products. This may account for the significant discrepancies between the T(206Pb/238U) and T(207Pb/235U) age values. RD238U was most probably lost via the migration of radioisotopes at the middle part and end of the 238U family (starting with 226Ra). The heavy Th, Pa, and U radioisotopes (234Th, 234Pa, 234U, and 230Th) that occur closer to the beginning of 238U decay, before 226Ra, only relatively insignificantly participated in the process. Our results show that the loss and migration of RD238U are, under certain conditions, the main (or even the only) process responsible for the distortion of the U-Pb system. 相似文献
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Joachim Hoefs Gunter Faure David H. Elliot 《Contributions to Mineralogy and Petrology》1980,75(3):199-203
Theδ18O (SMOW) values of the Kirkpatrick Basalt (Jurassic) on Mt. Falla, Queen Alexandra Range, vary between +6.3‰ and +8.6‰ The apparent enrichment of these rocks in18O excludes the possibility that they were altered by interaction with aqueous solutions of meteoric origin. Theδ18O values of the flows correlate significantly with the initial87Sr/86Sr ratios and all major elements. These correlations confirm the hypothesis that the basalt magma was contaminated by rocks of the continental crust through which it was extruded. Estimates of the chemical composition of the basalt magma and the contaminant, based on extrapolations of the new oxygen data, generally confirm earlier estimates based on extrapolations of initial87Sr/86Sr ratios. The87Sr/86Sr ratio of the uncontaminated basalt was 0.7093 which indicates that magma may have originated by melting either in old Rb-enriched lithospheric mantle under Antarctica or in the overlying crust, or both. 相似文献
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We report here a40Ar-39Ar age of 66.0 ± 0.9 Ma (2σ) for a reversely magnetised tholeiitic lava flow from the Bhimashankar Formation (Fm.), Giravali Ghat, western Deccan province,
India. This age is consistent with the view that the 1.8–2 km thick bottom part of the exposed basalt flow sequence in the
Western Ghats was extruded very close to 67.4 Ma. 相似文献
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Presence of young groundwater (post-1950) in the Goose River basin is demonstrated with 3H and 85Kr analyses. A total of 96 wells and four springs were sampled quarterly from 1999 to 2001 to determine the extent of any recent recharge and to what depth hydraulic continuity existed in the groundwatershed (33.3 km2). Recharge groundwater is less than 50 years in about 31% (3H) to 37% (85Kr) of sampled wells and 75% of sampled springs. Young groundwater ages are recorded in wells up to 320 m in depth within fractured- and arsenic-bearing crystalline bedrock. Total arsenic 10 g L–1 occurs significantly in drinking water with young groundwater flowing through the pumping well intervals. Astotal occurs in 89% (85Kr) to 93% (3H) of all wells with post-1950 groundwater ages. Young groundwater recharge and elevated geogenic arsenic were discovered only in the anatectic granitoids and migmatized country rock of the southwestern part of the Goose River basin. 相似文献
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Groundwaters of Primorye, including its coastal areas, were studied during the past ten years. The macro-and microelement composition of more than 130 samples showed that shallow groundwaters of southern Primorye with pH ranging between 5.4 and 8.4 contain oxygen (up to 10 mg/l) and typically have a mixed ionic composition. The microelement variations reflect both the natural features of the host rocks and possible anthropogenic pollution in the most populated areas. No seawater intrusions were recognized in the study areas, which is confirmed by the chemical composition of the waters, the oxygen and hydrogen isotopic composition of the groundwaters, the atmospheric precipitation, and the coastal seawaters of Primorye. In spite of the variations of individual components, the quality of the groundwaters used for potable purposes is rather satisfactory as compared to the Russian and the World Health Organization standards. At the same time, taking into account the increase of various microelements and biogenic components in the waters, the monitoring and control of the water composition is strongly recommended to preserve their potable quality. 相似文献
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C. J. Warren S. C. Sherlock S. P. Kelley 《Contributions to Mineralogy and Petrology》2011,161(6):991-1009
New single grain fusion and core-rim 40Ar/39Ar laserprobe phengite data from the Saih Hatat high-pressure terrane in NE Oman show that individual samples yield a range
of apparent ages which is similar to that previously reported from across the entire terrane. The majority of the determined
ages are older than the previously reported U-Pb zircon peak metamorphic age. Core to rim age variations within individual
grains range from no discernible difference across the grain to grains with older cores, or, rarely, older rims; some samples
manifest all three patterns. Numerical diffusion modelling shows that due to the peak temperature of ca. 550°C, the measured
apparent ages cannot be explained by simple cooling or by partial retention of crystallisation or detrital ages in an open
system. The age variability is better explained by spatially and temporally variable open or closed system behaviour at the
mm-cm scale coupled with pervasive and heterogeneously distributed excess argon. Anomalously old eclogite phengite 40Ar/39Ar ages are due either to internally derived 40Ar inherited from a K-bearing precursor, or externally derived 40Ar distributed by grain boundary fluids. Mica-rich schists within the eclogite boudins yield younger phengite ages, suggesting
excess argon was absent or diluted. Pelites hosting the eclogite appear to have been affected by later fluid ingress during
deformation and greenschist-facies overprint and yield very variable ages commonly with apparently older rims on younger cores.
The grain- and sample-scale age variations measured in Saih Hatat indicate that the grain boundary network in eclogite pods
was not an efficient transfer pathway for argon transport, whereas the grain boundary network in the surrounding pelites acted
as a more efficient pathway on the timescale of the metamorphic cycle. 相似文献
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The Baimazhai nickel deposit, Yunnan Province, China, is located in the southern part of the Sanjiang （Tri-river） alkali-rich intrusive rock belt （Sanjiang ARIR）. In this paper was conducted ^40Ar-^39Ar dating of two phlogopites in lamprophyres which are, as dikes, widely distributed in the orefield, and two plateau ages were acquired, i.e., 32.46±0.62 Ma and 32.01±0.60 Ma, respectively （averaging 32.23±0.60 Ma）. The ages are obviously younger than those of the ore-hosted complex and mineralization of the Baimazhai nickel deposit. In combination with the characteristics, it is indicated that lamprophyres in the orefield and those in the Sanjiang ARIR are similar in tectonic setting, mineral assemblage and geochemistry. It is considered that lamprophyres in the orefield are the important component of the Sanjiang ARIR, and the lamprophyres and ore-hosted complex in the orefield represent the products of two times of different magmatic activity from different mantle sources. On the other hand, the age of lamprophyres in the orefield is older than that of the strike-slip shearing of the Ailaoshan-Honghe fault belt, suggesting that the strike-slip shearing of the Ailaoshan-Honghe fault belt is not the factor leading to magmatic activity of lamprophyres in the orefield, while it is more possible that magmatic activity of the Sanjiang ARIR promoted strike-slip shearing of the fault belt. 相似文献
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Verónica Oliveros Gilbert Féraud Luis Aguirre Luis Ramírez Michel Fornari Carlos Palacios Miguel Parada 《Mineralium Deposita》2008,43(3):281-293
The 40Ar/39Ar geochronological method was applied to date magmatic and hydrothermal alteration events in the Mantos Blancos mining district
in the Coastal Cordillera of northern Chile, allowing the distinction of two separate mineralization events. The Late Jurassic
Mantos Blancos orebody, hosted in Jurassic volcanic rocks, is a magmatic-hydrothermal breccia-style Cu deposit. Two superimposed
mineralization events have been recently proposed. The first event is accompanied by a phyllic hydrothermal alteration affecting
a rhyolitic dome. The second mineralization event is related to the intrusion of bimodal stocks and sills inside the deposit.
Because of the superposition of several magmatic and hydrothermal events, the obtained 40Ar/39Ar age data are complex; however, with a careful interpretation of the age spectra, it is possible to detect complex histories
of successive emplacement, alteration, mineralization, and thermal resetting. The extrusion of Jurassic basic to intermediate
volcanic rocks of the La Negra Formation is dated at 156.3 ± 1.4 Ma (2σ) using plagioclase from an andesitic lava flow. The first mineralization event and associated phyllic alteration affecting
the rhyolitic dome occurred around 155–156 Ma. A younger bimodal intrusive event, supposed to be equivalent to the bimodal
stock and sill system inside the deposit, is probably responsible for the second mineralization event dated at ca. 142 Ma.
Other low-temperature alteration events have been dated on sericitized plagioclase at ca. 145–146, 125, and 101 Ma. This is
the first time that two distinct mineralization events have been documented from radiometric data for a copper deposit in
the metallogenic belt of the Coastal Cordillera of northern Chile.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
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Mineralization and alteration events at ten Miocene porphyry Cu and porphyry-related epithermal mineral deposits in southern,
central, and northern Ecuador were dated by means of molybdenite Re-Os, biotite and alunite 40Ar/39Ar, and titanite U-Pb geochronology. Most of these hydrothermal events show a spatio-temporal correlation with porphyry intrusion
emplacement as constrained by zircon U-Pb ages. The total age range for these events spans the 23.5–6.1 Ma period, without
displaying systematic along- or across-arc age distribution trends. While epithermal deposits tend to be spatially associated
with volcanic rocks of a similar age, porphyry Cu deposits in Ecuador are frequently spatially associated with deeper-seated
basement units and batholith-scale precursor intrusive systems assembled over ≥5 m.y. time periods. In most cases, formation
of the porphyry Cu deposits is related to the youngest magmatic (-hydrothermal) event in a given area, postdating batholith
construction at a regional scale. The majority of Miocene deposits occurs in southern Ecuador where areally extensive, post-mineralization
(late Miocene to recent) volcanic sequences with the potential to conceal mineralization at depth are lacking. Only few Miocene
deposits occur in northern-central Ecuador, where they mainly crop out in the Western Cordillera, west of the productive present-day
volcanic arc. The surface distribution of post-mineralization arc volcanism reflects along-arc variations in subducting slab
geometry. Porphyry Cu and epithermal deposits in Ecuador define a Miocene metallogenic belt broadly continuous with its coeval
counterpart in northern-central Peru. Although both belt segments were formed in an overall similar tectonomagmatic and metallogenic
setting, their respective metal endowments differ significantly. 相似文献
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NAVEEN GANDHI SANJEEV KUMAR S PRAKASH R RAMESH M S SHESHSHAYEE 《Journal of Earth System Science》2011,120(1):99-111
Various experiments involving the measurement of new, regenerated and total productivity using 15N and 13C tracers were carried out in the Bay of Bengal (BOB) and in the Arabian Sea. Results from 15N tracer experiments indicate that nitrate uptake can be underestimated by experiments with incubation time <4 hours. Indirect
evidence suggests pico- and nano-phytoplankton, on their dominance over microphytoplankton, can also influence the f-ratios.
Difference in energy requirement for assimilation of different nitrogen compounds decides the preferred nitrogen source during
the early hours of incubation. Variation in light intensity during incubation also plays a significant role in the assimilation
of nitrogen. Results from time course experiments with both 15N and 13C tracers suggest that photoinhibition appears significant in BOB and the Arabian Sea during noon. A significant correlation
has been found in the productivity values obtained using 15N and 13C tracers. 相似文献
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I. V. Chernyshev V. N. Golubev A. V. Chugaev G. V. Mandzhieva 《Doklady Earth Sciences》2016,470(2):1097-1099
The variations in 238U/235U values accompanying mobilization of U by fracture waters from uranium-bearing rocks, in which U occurs as a fine impregnation of oxides and silicates, were studied by the high-precision (±0.07‰) MC–ICP–MS method. Transition of U into the aqueous phase in the oxidized state U(VI) is accompanied by its isotope fractionation with enrichment of dissolved U(VI) in the heavy isotope 238U up to 0.32‰ in relation to the composition of the solid phases. According to the sign, this effect is consistent with the tendency of the behavior of 238U and 235U upon interaction of river waters with rocks of the catchment areas [11] and with the effect observed during oxidation of uraninite by the oxygen-bearing NaHCO3 solution [12]. 相似文献