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Low-temperature alteration of uranium–thorium bearing minerals and its significance in neoformation of radioactive minerals in stream sediments of Wadi El-Reddah, North Eastern Desert, Egypt

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Acta Geochimica 2020年第1期39卷 96-115页

作者： O.A.Ebyan H.A.Khamis A.R.Baghdady M.G.El-Feky N.S.Abed Geology Department Faculty of ScienceAin Shams UniversityCairo 11566Egypt Nuclear Materials Authority(NMA) P.O.Box 530El-MaadiCairoEgypt

The stream sediments of Wadi El Reddah(North Eastern Desert,Egypt)are geochemically and mineralogically investigated.Their content of radioactive and other heavy minerals is mainly represented by thorite,uranothorite,zircon,monazite,xenotime,columbite,fergusonite,and unknown rare earth elements(REEs)bearing minerals as well as cassiterite.Special emphasis on REE content of thorite,uranothorite,zircon and xenotime has been done to correlate them with the increase of uranium contents in these sediments.The key evidence for the presence lowtemperature alteration processes includes the presence of some zircon crystals as remnants after complete dissolution of the overgrowth zircon in severe acidic environment,the sulphur content,biogenic minerals,occurrence of unusual minerals as cassiterite pore filling in zircon,variation in the REEs content from the surrounding granites to the stream sediments and the abundance of monazite in the surrounding granites.Most minerals are partially and/or completely altered,which indicated by the pseudomorphism of zircon by xenotime,thorite,and uranothorite.

关键词： Zircon Thorite xenotime Radioactive minerals Low-temperature alteration Wadi El-Reddah

Mineralogy and geochemistry of Nb-,Ta-,Sn-,U-,Th-,and Zr-bearing granitic rocks from Abu Rusheid shear zones,South Eastern Desert,Egypt

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Chinese Journal Of Geochemistry 2011年第2期30卷 226-247页

作者： Ali M.A. Lentz D.R. Hall D.C. Nuclear Materials Authority P.O.530.El MaadiCairoEgypt Department of Geology New Brunswick UniversityUNBCanada Microscopy and Microanalysis Facility New Brunswick UniversityUNBCanada

Granite-hosted,Nb-,Ta-,Sn-,U-,Th-,and Zr(Hf)-bearing mineralization from the Abu Rusheid shear zones occurs about 97 km southwest of the town of Marsa Alam,South Eastern Desert,Egypt.The SSE-trending brittle-ductile Abu Rusheid shear zones crosscut the peralkalic granitic gneisses and cataclastic to mylonitic rocks(mylonite,protomlyonite,and ultramylonite).The northern shear zone varies in width from 1 to 3 m with a strike length of >500 m,and the southern shear zone is 0.5 to 8 m wide and >1 km long.These shear zones locally host less altered lamprophyre and locally sheared granitic aplite-pegmatite dykes.The rare-metal minerals,identified from the peralkalic granitic gneisses and cataclastic to mylonitic rocks are associated with muscovite,chlorite,quartz,fluorite,pyrite,magnetite,and rare biotite that are restricted to the Abu Rusheid shear zones;these are columbite-tantalite and pyrochlore(var.betafite) in the northern shear zone and ferrocolumbite in the southern shear zone.Cassiterite occurs as inclusions in the columbite-tantalite minerals.U-and Th-minerals(uraninite,thorite,uranothorite,ishikawaite,and cheralite) and Hf-rich zircon coexist.Magmatic(?) zircon contains numerous inclusions of rutile,fluorite,U-Th and REE minerals,such as uranothorite,cheralite,monazite,and xenotime.Compositional variations in Ta/(Ta+Nb) and Mn/(Mn+Fe) in columbite range from 0.07-0.42 and 0.04-0.33,respectively,and Hf contents in zircon from 1.92-6.46 of the two mineralized shear zones reflect the extreme degree of magmatic fractionation.Four samples of peralkalic granitic gneisses and cataclastic to mylonitic rocks from the southern shear zone have very low TiO2(0.02 wt%-0.04 wt%),Sr [(15-20)×10-6],and Ba [(47-78)×10-6],with high Fe2O3T(0.94 wt%-1.99 wt%),CaO(0.14 wt%-1.16 wt%),alkalis(9.2 wt%-10.1 wt%),Rb [(369-805)×10-6],Zr [(1033-2261)×10-6],Nb [(371-913)×10-6],U [(51-108)×10-6],Th [(36-110)×10-6],Ta [(38-108)×10-6],Pb [(39-364)×10-6],Zn [(21-424)×10-6],Y [(8-304)×10-6],Hf [(29-157)×10-6],and ∑REE [(64-304)×10-6],especia

关键词： uranium thorium zircon columbite-tantalite fluorite monazite xenotime age dating granitic gneisses South Eastern Desert Egypt

Linking gold mineralization to regional-scale drivers of mineral systems using in situ U-Pb geochronology and pyrite LA-ICP-MS element mapping

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Geoscience Frontiers 2019年第1期10卷 89-105页

作者： Imogen O.H.Fielding Simon P.Johnson Sebastien Meffre Jianwei Zi Stephen Sheppard Ross R.Large Birger Rasmusseng Department of Applied Geology Curtin University Geological Survey of Western Australia CODES ARC Centre of Excellence in Ore Deposits University of Tasmania State Key Lab of Geological Processes and Mineral Resources China University of GeosciencesWuhan John de Laeter Centre Curtin University Calidus Resources Ltd School of Earth Sciences The University of Western Australia

Proterozoic orogens commonly host a range of hydrothermal ores that form in diverse tectonic settings at different times. However, the link between mineralization and the regional-scale tectonothermal evolution of orogens is usually not well understood, especially in areas subject to multiple hydrothermal events.Regional-scale drivers for mineral systems vary between the different classes of hydrothermal ore, but all involve an energy source and a fluid pathway to focus mineralizing fluids into the upper crust. The Mount Olympus gold deposit in the Proterozoic Capricorn Orogen of Western Australia, was regarded as an orogenic gold deposit that formed at ca. 1738 Ma during the assembly of Proterozoic Australia. However,the trace element chemistry of the pyrite crystals closely resembles those of the Carlin deposits of Nevada,with rims that display solid solution gold accompanied by elevated As, Cu, Sb, Hg, and Tl, surrounding gold-poor cores. New SHRIMP UeP b dating of xenotime intergrown with auriferous pyrite and ore-stage alteration minerals provided a weighted mean^(207) Pb*/^(206) Pb* date of 1769 ± 5 Ma, interpreted as the age of gold mineralization. This was followed by two discrete episodes of hydrothermal alteration at 1727 ± 7 Ma and 1673 ± 8 Ma. The three ages are linked to multiple reactivation of the crustal-scale Nanjilgardy Fault during repeated episodes of intracratonic reworking. The regional-scale drivers for Carlin-like gold mineralization at Mount Olympus are related to a change in tectonic regime during the final stages of the intracratonic 1820 -1770 Ma Capricorn Orogeny. Our results suggest that substantial sized Carlin-like gold deposits can form in an intracratonic setting during regional-scale crustal reworking.

关键词： Geochronology xenotime SHRIMP LA-ICP-MS Gold mineralization Capricorn orogen

Monazite and xenotime U-Th-Pb geochronology by ion microprobe:dating highly fractionated granites at Xihuashan tungsten mine,SE China

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Monazite and xenotime U-Th-Pb geochronology by ion microprob...

In situ U-Pb dating of xenotime by laser ablation(LA)-ICP-MS

中国科学院地质与地球物理研究所2013年度（第13届）...

作者： Q.L.Li X.H.Li Z.W.Lan C.L.Guo Y.N.Yang Y.Liu G.Q.Tang State Key Laboratory of Lithospheric Evolution Institute of Geology and GeophysicsChinese Academy of Sciences Institute of Mineral Resources Chinese Academy of Geological Sciences University of Chinese Academy of Sciences

Zircon,monazite,and xenotime have proven to be valuable chronometers for various geological processes due to their commonly high-U-Th and low common Pb contents.However,zircons that have crystallized in highly fractionated granites often have such high-U contents that radiation damage can lead to scattered U-Pb ages when measured with secondary ion mass spectrometry(SIMS). In this study,monazite and xenotime were separated from a number of highly fractionated granites at the Xihuashan tungsten mine,Southeast China,for alternative dating methods by SIMS.For monazite analysis,obvious excess Pb signal(mainly from interference of ThNdO) was observed in high-Th(>2 wt%) monazite,which hinders Pb-based common Pb corrections. A Pb-based common Pb correction method was used instead.By employing power law relationships between Pb/U versus UO/U,Pb/Th versus ThO/Th and suitable exponentials,monazites with TI1O2 contents in the range of～3-19%do not exhibit this matrix effect.Independent SIMS U-Pb ages and Th-Pb ages of three phases of Xihuashan granite samples were consistent with each other and yielded dates of 158.7±0.7,158.0±0.7,and 156.9±0.7 Ma,respectively.xenotime does show marked matrix effects due to variations of U,Th,and Y[or total rare earth element(REE),referred as ZREE hereafter]contents. Suitable correction factors require end-member standards with extremely high or low U,Th,and Y(or ZREE) contents. No excess Pb was observed,indicating that the Pb-based common Pb correction method is feasible. Independent Pb/Pb ages can be obtained,although multi-collector mode is necessary to improve precision.The main difficulties with dating xenotime are when high-Th (U) mineral inclusions are ablated.We can identify when this occurs,however,by comparing the measured UO/U and ThO/Th with those in xenotime standards.Three xenotime samples from the first phase of Xihuashan granite yielded a weighted mean 207Pb/Pb date of 159.5±4.4 Ma(MSWD = 1.0) and a Pb/U date of 159.4±0.9 Ma(MSWD =1.6),which are consistent with monazite U-Pb

关键词： SIMS Monazite xenotime Zircon U-Pb dating Highly fractionated granites

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In situ U-Pb dating of xenotime by laser ablation(LA)-ICP-MS