Arid
DOI10.2465/jmps.080506
Role of geochemical alteration on the formation of secondary Zr- and U-bearing minerals in El Atshan trachyte, central Eastern Desert, Egypt
El-Naby, Hamdy H. Abd1,2
通讯作者El-Naby, Hamdy H. Abd
来源期刊JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES
ISSN1345-6296
EISSN1349-3825
出版年2009
卷号104期号:1页码:37-51
英文摘要

El Atshan area, situated in the central Eastern Desert of Egypt, is a good location for studying the influence of high- and low-T alterations on the formation of Zr- and U-bearing minerals within a trachyte sill. These minerals are mainly represented by an unidentified secondary Zr-rich silicate mineral, betafite, and liandratite. The unidentified Zr-rich silicate mineral is considered to be an alteration product of the precursor zirconolite during high-T alteration. This is indicated by the changes in the composition marked by an increase in the amount of hydration (H2O), Si, and U and a decrease in the amount of Ca, Ti, Nb, and Fe. The morphology of this unidentified mineral is similar to that of zirconolite. For seven oxygen atoms, the calculated formula of the unidentified Zr-rich silicate mineral is (Si1.45U0.18Ca0.32Pb0.01Nb0.06Zr1.18Hf0.01Fe0.06Al0.08Ti0.11P0.09Y0.05REE0.09)(Sigma 3.7)O-7. With more extensive alteration, it was found that the unidentified secondary Zr-rich silicate mineral was unstable and it underwent re-equilibration with U-rich fluid, which led to alterations in betafite. The two possible mechanisms responsible for the alteration of the unidentified Zr-rich silicate mineral to betafite are as follows: (1) the dissolution of the unidentified Zr-rich silicate mineral and precipitation of betafite and (2) the ion-exchange between partially to fully amorphized zones and the U-rich fluid. Such alteration is indicated by a marked increase in the amount of U, Ti, and Nb and a decrease in the amount of Zr, Si, Ca, P, Y, and Sigma REE. The single substitution of U4+ <-> Zr4+ and the coupled substitution of (U4+ + Ti4+ + Nb5+) <-> (Zr4+ + Si4++ Ca2+ + P5+ + Y3+ + Sigma REE3+) appear to be the main causes for the formation of betafite. For 2.00 B-site cations, the calculated formula of the betafite is (A)(U0.44Ca0.25REE0.05Y0.03Pb0.02)(Sigma 0.79)(B)(Si0.79Zr0.69Ti0.23Nb0.12Al0.06Fe0.05P0.03V0.02Hf0.01)Sigma O-2.0(7). Betafite was altered to liandratite in the late low-T alteration stage. For 2.00 Nb-site cations, the calculated formula of the liandratite is (U)(U1.35Ca0.41Pb0.04REE0.04Y0.01)(Sigma 1.86)(Nb)(Ti(0.67)Si(0.46)Nb(0.40)Zr(0.26)e(0.09)V(0.08)Al(0.03)Ta(0.01))Sigma O-2.0(8). Among different uranium complexes, the influence of fluoride on the solubility and mobility of uranium is confirmed.


英文关键词Egypt Unidentified Zr-rich silicate mineral Betafite Liandratite Alteration
类型Article
语种英语
国家Saudi Arabia ; Egypt
收录类别SCI-E
WOS记录号WOS:000263905200004
WOS关键词PYROCHLORE GROUP ; ION IRRADIATION ; ZIRCONOLITE ; BETAFITE ; ELEMENTS
WOS类目Mineralogy
WOS研究方向Mineralogy
资源类型期刊论文
条目标识符http://119.78.100.177/qdio/handle/2XILL650/161690
作者单位1.King Abdulaziz Univ, Fac Earth Sci, Jeddah 21589, Saudi Arabia;
2.Nucl Mat Author, Cairo, Egypt
推荐引用方式
GB/T 7714
El-Naby, Hamdy H. Abd. Role of geochemical alteration on the formation of secondary Zr- and U-bearing minerals in El Atshan trachyte, central Eastern Desert, Egypt[J],2009,104(1):37-51.
APA El-Naby, Hamdy H. Abd.(2009).Role of geochemical alteration on the formation of secondary Zr- and U-bearing minerals in El Atshan trachyte, central Eastern Desert, Egypt.JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES,104(1),37-51.
MLA El-Naby, Hamdy H. Abd."Role of geochemical alteration on the formation of secondary Zr- and U-bearing minerals in El Atshan trachyte, central Eastern Desert, Egypt".JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES 104.1(2009):37-51.
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