LA–ICP–MS Isotopic U–Pb Age of Zircon from the Eldzhurty Granites and Rhyolites at the Tyrnyauz Mo–W Deposit (North Caucasus,Russia)

Doklady Earth Sciences - The isotopic U–Pb ages are estimated for zircons (for the first time by the LA–ICP–MS method) from biotite (Eldzhurty) granites and for the first time...     

Late Paleozoic Age of Intrusive Rocks from the “Trondhjemite” Massif of the Tyrnyauz W–Mo Deposit (North Caucasus,Russia): The First Results of U–Pb Isotope Dating of Zircon (LA–ICP–MS Method)

Doklady Earth Sciences - The first data of U–Pb isotopic study (LA–ICP–MS method) of zircon from tonalite–granodiorite forming a dominant part of the...     

First Data on the U–Pb Isotopic Age for Zircon (LA-ICP-MS Method) from Leucocratic Granites of the Tyrnyauz Mo–W Deposit (North Caucasus,Russia)

Doklady Earth Sciences - The first data of a U–Pb isotopic study (LA-ICP-MS method) of zircon from leucocratic granites of the giant Tyrnyauz Mo–W deposit (North Caucasus) are...     

Garnet U–Pb Age of Skarns from Dashkesan Deposit (Lesser Caucasus)

Doklady Earth Sciences - The results of the U–Pb geochronological study of garnet from scarns of the Dashkesan deposit are reported. The first “direct” estimate of the age of the...     

Age and Sources of Metasandstone of the Chiney Subgroup (Udokan Group,Aldan Shield): Results of U–Th–Pb Geochronological (LA–ICP–MS) and Nd Isotope Study

Results of U–Th–Pb LA–ICP–MS analysis of detrital zircons from metasandstones of the Chiney Subgroup (Udokan Group, Aldan Shield) have been obtained. It has been revealed that rocks of the Paleoproterozoic (about 1.90, 1.98, and 2.50 Ga) and Neoarchean (2.55 and 2.72 Ga) were their provenance sources. Deposition of the Chiney Subgroup occurred in the interval 1.87–1.90 Ga and was separated in time from the accumulation of the Kodar Subgroup siliciclastics (2.1–2.3 Ga).     

LA–ICP–MS U–Pb Geochronology of Detrital Zircon in the Guanzhong Basin, China and Its Tectonic Response

正Objective The Guanzhong Basin in the transitional zone of the Qinling orogenic belt and the southern margin of the Ordos Basin has been extensively studied in recent years.Although some results have been obtained,some problems such as whether the materials from the North China craton and the Qinling orogenic belt are detrital sedimentary rocks of the Guanzhong Basin still remain unresolved.     

U–Pb LA–ICP–MS Age of Detrital Zircons from the Lower Riphean and Upper Vendian Deposits of the Luga–Ladoga Monocline

The results of LA–ICP–MS U–Pb analyses of detrital zircons from the Precambrian deposits of Luga–Ladoga monocline are discussed. The age spectra of the zircons separated from the Riphean to Upper Vendian sandstones from the Shotkusa-1 well demonstrate dominance of the Paleo- and Mesoproterozoic grains while the Archaean zircons are subordinate. The Riphean debris sources were local swells of the Northern Ladoga basement. The sequence interval presumably corresponding to the Vasilieostrov Formation (Upper Vendian) has yielded not only Paleo- and Mesoproterozoic zircon ages, but Neoproterozoic as well, implying a Timanide provenance: these zircons (527 ± 9 and 516 ± 13 Ma) allow deposition of a significant part of the Shotkusa-1 sequence at the very beginning of the Cambrian.     

Age and Stratigraphic Position of Sedimentary Sequences of the Bagrush Mountains (Southern Urals) Based on the Results of U–Pb Dating (LA–ICP–MS) of Detrital Zircons

Doklady Earth Sciences - In order to determine the provenance and age of terrigenous-carbonate stratified units exposed in the region of Bagrush Mountains, Bashkirian uplift, U–Pb dating of...     

New Data on the Age of Neoproterozoic Volcanic Rocks of the Isakovka Terrane,Sayan–Yenisei Accretion Belt (U–Pb,Zircon)

Doklady Earth Sciences - A Late Neoproterozoic U–Pb zircon age is established for the first time for arc metadacites (691 ± 8.8 Ma) and basalts (572 ± 6.5 Ma) from the...     

Genesis of the Weiquan Ag–Polymetallic Deposit in East Tianshan, China: Evidence from Zircon U–Pb Geochronology and C–H–O–S–Pb Isotope Systematics

The Weiquan Ag-polymetallic deposit is located on the southern margin of the Central Asian Orogenic Belt and in the western segment of the Aqishan-Yamansu arc belt in East Tianshan,northwestern China. Its orebodies, controlled by faults, occur in the lower Carboniferous volcanosedimentary rocks of the Yamansu Formation as irregular veins and lenses. Four stages of mineralization have been recognized on the basis of mineral assemblages, ore fabrics, and crosscutting relationships among the ore veins. Stage I is the skarn stage(garnet + pyroxene), Stage Ⅱ is the retrograde alteration stage(epidote + chlorite + magnetite ± hematite 士 actinolite ± quartz),Stage Ⅲ is the sulfide stage(Ag and Bi minerals + pyrite + chalcopyrite + galena + sphalerite + quartz ± calcite ± tetrahedrite),and Stage IV is the carbonate stage(quartz + calcite ± pyrite). Skarnization,silicification, carbonatization,epidotization,chloritization, sericitization, and actinolitization are the principal types of hydrothermal alteration. LAICP-MS U-Pb dating yielded ages of 326.5±4.5 and 298.5±1.5 Ma for zircons from the tuff and diorite porphyry, respectively. Given that the tuff is wall rock and that the orebodies are cut by a late diorite porphyry dike, the ages of the tuff and the diorite porphyry provide lower and upper time limits on the age of ore formation. The δ~(13)C values of the calcite samples range from-2.5‰ to 2.3‰, the δ~(18)O_(H2 O) and δD_(VSMOW) values of the sulfide stage(Stage Ⅲ) vary from 1.1‰ to 5.2‰ and-111.7‰ to-66.1‰, respectively,and the δ~(13)C, δ~(18)O_(H2 O) and δD_(V-SMOW) values of calcite in one Stage IV sample are 1.5‰,-0.3‰, and-115.6‰, respectively. Carbon, hydrogen, and oxygen isotopic compositions indicate that the ore-forming fluids evolved gradually from magmatic to meteoric sources. The δ~(34)S_(V-CDT) values of the sulfides have a large range from-6.9‰ to 1.4‰, with an average of-2.2‰, indicating a magmatic source, possibly with sedimentary contributions. The ~(206)Pb/~(204)Pb, ~(207)Pb/~(204)Pb, and ~(208)Pb/~(204)Pb ratios of the sulfides are 17.9848-18.2785,15.5188-15.6536, and 37.8125-38.4650, respectively, and one whole-rock sample at Weiquan yields~(206)Pb/~(204)Pb,~(207)Pb/~(204)Pb, and ~(208)Pb/~(204)Pb ratios of 18.2060, 15.5674, and 38.0511,respectively. Lead isotopic systems suggest that the ore-forming materials of the Weiquan deposit were derived from a mixed source involving mantle and crustal components. Based on geological features, zircon U-Pb dating, and C-H-OS-Pb isotopic data, it can be concluded that the Weiquan polymetallic deposit is a skarn type that formed in a tectonic setting spanning a period from subduction to post-collision. The ore materials were sourced from magmatic ore-forming fluids that mixed with components derived from host rocks during their ascent, and a gradual mixing with meteoric water took place in the later stages.     

In situ U–Pb isotopic dating of columbite–tantalite by LA–ICP–MS

Columbite–tantalite (Coltan) is the most important niobium (Nb)- and tantalum (Ta)-bearing economic mineral, commonly occurring in rare metal granite and pegmatite, alkaline granite, syenite and carbonatite. Its high U but low common Pb contents make it an ideal mineral for U–Pb isotopic dating of Nb–Ta mineralization. In order to establish a feasible coltan dating method by in situ laser-ablation (LA) ICP–MS, we determined the U–Pb ages of five coltan samples from different pegmatites and rare-metal granites in China. In order to evaluate the potential matrix effect between different minerals, a 91500 zircon was used as external standard during analyses. The results show that, compared to the recommended ages, approximately 7–15% younger ages were yielded for the analyzed coltan samples in both single spot and line raster scan analytical methods, indicating a significant matrix effect between coltan and zircon. However, by using a coltan standard from Namibia (Coltan139), the coltan sample from Dahe pegmatite (SNNT) has a weighted mean ²⁰⁶Pb/²³⁸U age of 363 ± 4 Ma (2σ, n = 25) and 357 ± 5 Ma (2σ, n = 20) in single spot and line raster scan analytical methods, respectively; the coltan samples from Altai No.3 pegmatite (713-79), Yichun topaz-lepidolite granite (Yi-1) and Huangshan albite granite (LS-15) have weighted mean ²⁰⁶Pb/²³⁸U ages of 218 ± 2 Ma (2σ, n = 20), 160 ± 1 Ma (2σ, n = 20) and 130 ± 1 Ma (2σ, n = 20), respectively, in single spot mode. These ages agree well with the previously published data, and hence support the reliability of our analytical method. Although the analyzed coltan minerals show a large variation of chemical compositions, no significant matrix effect was observed, which suggests that a coltan material should be used as an external standard for U–Pb dating of coltan by LA–ICP–MS. Using the established analytical protocol, we date the Nanping pegmatite (NP155), a main Nb–Ta deposit in China without known age, and obtain a weighted mean ²⁰⁶Pb/²³⁸U age of 391 ± 4 Ma (2σ, n = 20), which is considered as the best estimation of Nb–Ta mineralization time in the area.     

First Results of U–Pb LA–ICP–MS Isotope Dating of Detrital Zircons from Arkose Sandstone of the Biryan Subformation of Zilmerdak Formation (Upper Riphean,South Urals)

Detrital zircons (DZs) from arkose sandstones of the Upper Riphean Zilmerdak Formation (Southern Urals) yielded ages in the range of 3039–964 Ma. Grains with Late Karelian and Early and Middle Riphean ages compose 35, 34, and 26% of the total number of the analyzed zircons, respectively. This is similar to the age spectra of the Vendian sandstones (Asha Group), but it differs significantly from the age distribution typical of the Riphean stratotype sandstones.     

Preliminary Understanding of Ore Genesis of Zhaxikang Pb–Zn–Ag–Sb Deposit in the North Himalaya

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Zircon U／Pb Dating of Cretaceous Adakitic Volcanic Rocks in the Eastern Part of North Dabie Mountains

1IntroductionMostgeologistshaveacceptedthattheQinling Dabieorogenicbeltistheproductofcontinentaldeepsubduction (Okayetal.,1993;Cong ,B .etal.,1995 ;Hackeretal.,1995 ;DongShuwenetal.,1993) .Butasthebiggest scaleUHPmetamorphicbeltintheworld ,thereactionbetweenthecrustandthemantleatthepost orogenicstageandtheexhumation ,upliftinganddenudationoftheorogenicbeltarethecomplexdynamicprocesses .ItwasreportedpreviouslythatsomeCretaceousvolcanicrocksexistinthemiddleoftheDabieMountains (GuanYuncaiet…     

The U–Pb LA-SF-ICP-MS Age of Zircon from Metaplagiogranite of the Kharbei Metamorphic Complex (Polar Urals)

Doklady Earth Sciences - For timing of endogenous events in the Kharbei metamorphic complex (Polar Urals), U–Pb isotopic dating of zircons from garnet–clinozoisite–twomica...     

First Data on the Age (U–Pb,SHRIMP-II) and Composition of Zircon from the Unique Yarega Oil–Titanium Deposit,South Timan

Doklady Earth Sciences - Isotope–geochemical study of zircon from leucoxene–quartz sandstone of the Yarega deposit in South Timan was conducted for the first time using the Sensitive...     

Mineral Associations and Mo–W Ore Types of the Slepaya Zalezh’ Orebody at the Tyrnyauz Deposit

Geology of Ore Deposits - Slepaya Zalezh’, the largest orebody of the Tyrnyauz Mo–W deposit, is considered a first-priority object should mining operations at the deposit be resumed....     

New Data on the Age of Magmatic Events in Oloy Tectonic Zone,West Chukotka Area (Evidences from Zircon U–Pb Dating)

Doklady Earth Sciences - The following U–Pb ages (Ma) were obtained for zircons from volcanic rocks and granitoids representing various complexes of the Nembonda Depression (the Anadyr...     

Zircon from Gabbroids of the Shaka Ridge (South Atlantic): U–Pb Age,Oxygen Isotope Ratios,and Trace Element Composition

Geology of Ore Deposits - The paper presents the results of U–Pb SHRIMP-II dating and isotope-geochemical data on zircon xenocrysts extracted from igneous rocks of the Shaka Ridge, South...     

Age and Sources of Metasedimentary Rocks of the Tokur Terrane of the Mongol–Okhotsk Fold Belt: Results of U–Pb and Lu–Hf Isotope Studies

Doklady Earth Sciences - This paper presents the results of U–Pb (LA-ICP-MS) and Lu–Hf isotope studies of detrital zircons from the presumably Permian meta sedimentary rocks of the...