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971.
N.A. Gibsher A.A. Tomilenko A.M. Sazonov T.A. Bul’bak M.O. Khomenko M.A. Ryabukha E.O. Shaparenko S.A. Sil’yanov N.A. Nekrasova 《Russian Geology and Geophysics》2018,59(8):983-996
The Eldorado low-sulfide gold-quartz deposit, with gold reserves of more than 60 tons, is located in the damage zone of the Ishimba Fault in the Yenisei Ridge and is hosted by Riphean epidote-amphibolite metamorphic rocks (Sukhoi Pit Group). Orebodies occur in four roughly parallel heavily fractured zones where rocks were subject to metamorphism under stress and heat impacts. They consist of sulfide-bearing schists with veins of gray or milky-white quartz varieties. Gray quartz predominating in gold-bearing orebodies contains graphite and amorphous carbon identified by Raman spectroscopy; the contents of gold and amorphous carbon are in positive correlation. As inferred from thermobarometry, gas chromatography, gas chromatography-mass spectrometry, and Raman spectroscopy of fluid inclusions in sulfides, carbonates, and gray and white quartz, gold mineralization formed under the effect of reduced H2O-CO2-HC fluids with temperatures of 180 to 490 °C, salinity of 9 to 22 wt.% NaCl equiv, and pressures of 0.1 to 2.3 kbar. Judging by the presence of 11% mantle helium (3He) in fluid inclusions from quartz and the sulfur isotope composition (7.1-17.4‰ δ34S) of sulfides, ore-bearing fluids ascended from a mantle source along shear zones, where they “boiled”. While the fluids were ascending, the metalliferous S- and N-bearing hydrocarbon (HC) compounds they carried broke down to produce crystalline sulfides, gold, and disseminated graphite and amorphous carbon (the latter imparts the gray color to quartz). Barren veins of milky-white quartz formed from oxidized mainly aqueous fluids with a salinity of < 15 wt.% NaCl equiv at 150-350 °C. Chloride brines (> 30 wt.% NaCl equiv) at 150-260 °C impregnated the gold-bearing quartz veins and produced the lower strata of the hydrothermal-granitoid section. The gold mineralization (795-710 Ma) was roughly coeval to local high-temperature stress metamorphism (836-745 Ma) and intrusion of the Kalama multiphase complex (880-752 Ma). 相似文献
972.
973.
974.
M. V. Charykova E. L. Fokina V. G. Krivovichev O. S. Yakovenko E. V. Klimova V. V. Semenova 《Geology of Ore Deposits》2015,57(7):570-578
The aim of this study is the experimental investigation of the synthetic analogs of cobaltomenite, CoSeO3 ? 2H2O, ahlfeldite, NiSeO3 ? 2H2O, members of the cobaltomenite–ahlfeldite solid solution series (Ni x Co1–x )SeO3 ? 2H2O, and singularities of their dehydration and dissociation. The intermediate members of the cobaltomenite (CoSeO3 ? 2H2O)–ahlfeldite (NiSeO3 ? 2H2O) series have been synthesized and studied with a combination of X-ray diffraction, scanning electron microscopy, and the simultaneous application of thermogravimetry (TG) and differential scanning calorimetry (DSC) within the temperature range from 25 to 640°C. The complete solid solution series corresponds to the monoclinic space group P21/n. Unit-cell dimensions decrease in all crystallographic directions as the amount of Ni increases. The angle β increases from 98.82(1) (cobaltomenite) to 99.05(1)° (ahlfeldite). It has been established that CoSeO3 ? 2H2O and NiSeO3 ? 2H2O dehydrate at 120–340°C through two stages apparently corresponding, to the formation of intermediate hydrated species CoSeO3 ? H2O and NiSeO3 ? 1/3H2O. The reaction enthalpies for each dehydration stage of CoSeO3 ? 2H2O and NiSeO3 ? 2H2O have been determined. Changes of the unit-cell dimensions and dehydration temperatures are rationalized in terms of the Co and Ni site occupancy in the structure of the cobaltomenite–ahlfeldite solid-solution series members. 相似文献
975.
976.
Colin K. Ballantyne John O. Stone 《Boreas: An International Journal of Quaternary Research》2015,44(2):277-287
Trimlines separating glacially abraded lower slopes from blockfield‐covered summits on Irish mountains have traditionally been interpreted as representing the upper limit of the last ice sheet during the Last Glacial Maximum (LGM). Cosmogenic 10Be exposure ages obtained for samples from glacially deposited perched boulders resting on blockfield debris on the summit area of Slievenamon (721 m a.s.l.) in southern Ireland demonstrate emplacement by the last Irish Ice Sheet (IIS), implying preservation of the blockfield under cold‐based ice during the LGM, and supporting the view that trimlines throughout the British Isles represent former englacial thermal regime boundaries between a lower zone of warm‐based sliding ice and an upper zone of cold‐based ice. The youngest exposure age (22.6±1.1 or 21.0±0.9 ka, depending on the 10Be production rate employed) is statistically indistinguishable from the mean age (23.4±1.2 or 21.8±0.9 ka) obtained for two samples from ice‐abraded bedrock at high ground on Blackstairs Mountain, 51 km to the east, and with published cosmogenic 36Cl ages. Collectively, these ages imply (i) early (24–21 ka) thinning of the last IIS and emergence of high ground in SE Ireland; (ii) relatively brief (1–3 ka) glacial occupation of southernmost Ireland during the LGM; (iii) decoupling of the Irish Sea Ice Stream and ice from the Irish midlands within a similar time frame; and (iv) that the southern fringe of Ireland was deglaciated before western and northern Ireland. 相似文献
977.
D. E. Martínez O. M. Quiroz Londoño H. E. Massone P. Palacio Buitrago L. Lima 《Environmental Earth Sciences》2012,65(2):411-420
Fluoride pollution is a widespread problem in Argentina, as it is in many areas of the World. Former investigations have demonstrated
that the dissolution of volcanic glass disseminated in the loess-like sediments is the main source of fluoride in the Argentine
pampas. Nevertheless, fluoride distribution is erratic and the factors controlling it are not yet well-known. A large amount
of hydrochemical data collected in the Quequen Grande river catchment is used in order to contribute to the understanding
of fluoride distribution and mobility in groundwater in the Argentine pampas. The Quequen Grande river catchment is 10,000 km2. It extends between two low hills ranges of Precambrian metamorphic rocks and sedimentary Paleozoic rocks, filled by a thick
sequence of Cenozoic sediments, mainly silts and silt-clayed, with sand layers. These sediments form a multilayer phreatic
aquifer, which is recharged from precipitation infiltration, discharging through streams directly into the sea. Fluoride concentration
in surface water (n = 353) ranges between 0 and 6.5 mg/l, with an average value of 2.14 mg/l. Groundwater concentration (n = 135) is from 0 up to 5.7 mg/l, with an average of 1.84 mg/l. Considering the statistic distribution of fluoride, two groups
of samples can be determined. A dominant group between 0 and 3 mg/l, with a mean value around 1.5 mg/l, corresponding to samples
widely distributed in the catchment; and a second one group with fluoride contents between 3 and 6 mg/l, corresponding to
a smaller area in the central-west border. Two different sources are proposed. Volcanic glass dissolution is responsible for
dominant values in the catchment, while the weathering of biotite from the Paleozoic bedrock can be assumed to account for
the higher concentrations in the second group. 相似文献
978.
Cüneyt Akal Osman Candan O. Ersin Koralay Roland Oberhänsli Fukun Chen Dejan Prelević 《International Journal of Earth Sciences》2012,101(1):177-194
Afyon Zone, which was derived from the Anatolide–Tauride platform during closure of the Neo-Tethys, is made up of pre-Mesozoic
basement and unconformably overlying Triassic–Early Tertiary cover series. The Afyon Zone contains widespread metavolcanic
rocks, which are dominated by rhyolite, dacite, and trachyandesite. They form a distinct volcanic succession, which is separated
from the underlying Silurian–Lower Carboniferous metacarbonates and meta-siliciclastics by a regional unconformity. Trachyandesitic
metavolcanics are made up of massive lava flows, pyroclastics and epiclastics, less frequently, domes and dikes, which were
developed on a deeply eroded subaerial landmass. U/Pb and Pb/Pb zircon geochronology yielded Lower Triassic (~250 Ma) ages,
which are interpreted as extrusion age of trachyandesitic volcanics. Based on the stratigraphic, geochronological, and geochemical
data, we suggest that these Lower Triassic magmatic rocks represent an extensional tectonic setting on the northern active
margin of the Gondwana, which led to the development of the northern branch of the Neo-Tethys. 相似文献
979.
A.-M. Ertel A. Lupo N. Scheifhacken T. Bodnarchuk O. Manturova T. U. Berendonk T. Petzoldt 《Environmental Earth Sciences》2012,65(5):1459-1473
A pronounced pollution of surface water bodies in the Western Bug River Basin, Ukraine, has been caused by outdated or overloaded
wastewater treatment plants, agriculture, industry and coal mining. These pressures have led to a generally poor state of
both chemical and microbiological variables creating health risks of various kinds. The state of surface water quality for
the Western Bug and five main tributaries was assessed by measuring physical, chemical and microbiological indicators during
field campaigns in autumn 2009 and spring 2010. Longitudinal profiles were sampled to identify major sources of pollution
and to reveal dominant processes of matter turnover. In addition, the occurrence of antibiotic resistant strains in isolates
from stations along the Bug River was investigated. Results clearly underpin the negative impact of the Poltva River as a
major source of pollution for the Bug River and further outline an elevated potential health risk from pathogenic bacteria
originating from this source. Despite these devastating impacts, a high elimination potential of the Bug River with respect
to primary organic loads as well as elimination of pathogenic bacteria was observed particularly at Dobrotvir Reservoir. Further
downstream, pollution is kept high because of untreated waste effluents and phytoplankton mass developments due to high phosphorus
concentrations. 相似文献
980.
用ICP-MS技术测定了位于珠江口西岸香港西贡滨珊瑚在1991~2002年(分辨率达到0.5a)的稀土元素(REE)含量。实验结果显示香港滨珊瑚REE具有Ce负异常、重稀土富集这种典型的海水相分布模式。香港滨珊瑚中REE含量处于目前已见报道中的高值范围,与巴布亚新几内亚珊瑚的REE含量相当。通过与不同地区的比较,香港珊瑚高REE含量很可能就是毗邻的珠江水体高REE的直接反映,而且同南海北缘半封闭边缘海的性质有关。香港珊瑚REE的来源主要为珠江口及其相邻的陆缘沉积物。此外,1991~2002年香港珊瑚REE含量年际下降趋势十分明显,Ce负异常和重稀土富集的程度也呈加剧的趋势,分布模式向海水相转化。REE含量与海平面的年际变化之间有显著的负相关关系(r=-0.7~-0.9),而且重稀土与海平面的相关系数优于轻稀土。上述结果揭示了热带滨珊瑚对近期全球变暖、极冰融化和海水膨胀所引起的海平面快速上升的响应。 相似文献