Arid
DOI10.1016/j.oregeorev.2009.02.006
High and low temperature alteration of uranium and thorium minerals, Um Ara granites, south Eastern Desert, Egypt
El-Naby, Hamdy H. Abd
通讯作者El-Naby, Hamdy H. Abd
来源期刊ORE GEOLOGY REVIEWS
ISSN0169-1368
EISSN1872-7360
出版年2009
卷号35期号:3-4页码:436-446
英文摘要

The Urn Ara area, in the south Eastern Desert of Egypt contains a number of uranium occurrences related to granitic rocks. U-rich thorite, thorite and zircon are the main primary uranium- and thorium-bearing minerals found in mineralized zones of the Um Ara alkali-feldspar granites; uranophane is the most common secondary uranium mineral. U-rich thorite contains blebs of galena, has rims of uranophane and contains inclusions of Zr-rich thorite. Electron probe microanalysis (EPMA) provides an indication of a range of solid solution between thorite and zircon, in which intermediate phases, such as Th-rich zircon and Zr-rich thorite, were formed. These phases have higher sum of all cations per formula (2.05 to 2.06 apfu, for 4 oxygen atoms) than that of ideal thorite and zircon. This is attributed to the presence of substantial amount of interstitial cations such its Ca, U and Al in these phases. Some zircon grains are stoichiometric in composition, other altered grains display lower SiO2 and ZrO2 contents. Enrichment of Th and U in altered zircon preferentially involves coupled substitution (Ca2+ + (Th,U)(4+) <-> 2Zr(4+) + 2Si(4+)), implying that significant U and Th may enter the Zr and Si position in zircon. Negative correlation of Zr vs. Hf and Al may indicate that Hf and Al have been introduced to the zircon during later fluid alteration rather than during the primary magmatic event. A two-stage metallogenetic model is proposed for the alteration processes and origin of U- and Th-bearing minerals in the Urn Ara alkali-feldspar granite: 1) the first stage was dominated by hydrothermal alteration and accompanied by albitization, k-feldspathization, desilicification, chloritization, hematitization, silicification, argillization, fluoritization and corrosion of primary U-bearing minerals. Solid-solution between thorite and zircon occurred during this stage. The second stage occurred at the near-surface profile where circulating meteoric water played an important role in mobilizing the early formed primary U-bearing minerals. Uranium was likely transported as a calcium uranyl carbonate complexes. When these complexes lost their stabilities by precipitation of calcite, they decomposed in the presence of silica to form uranophane. (C) 2009 Elsevier B.V. All rights reserved.


英文关键词Egypt Um Ara U-rich thorite Thorite Zircon Uranophane Alteration
类型Review
语种英语
国家Egypt
收录类别SCI-E
WOS记录号WOS:000266762300011
WOS关键词COMPLEX-FORMATION ; SOLID-SOLUTIONS ; ZIRCON ; DEPOSITS ; ORE ; PARAGENESIS ; ERZGEBIRGE ; MOBILITY ; GERMANY ; ORIGIN
WOS类目Geology ; Mineralogy ; Mining & Mineral Processing
WOS研究方向Geology ; Mineralogy ; Mining & Mineral Processing
资源类型期刊论文
条目标识符http://119.78.100.177/qdio/handle/2XILL650/162093
作者单位Nucl Mat Author, Cairo, Egypt
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El-Naby, Hamdy H. Abd. High and low temperature alteration of uranium and thorium minerals, Um Ara granites, south Eastern Desert, Egypt[J],2009,35(3-4):436-446.
APA El-Naby, Hamdy H. Abd.(2009).High and low temperature alteration of uranium and thorium minerals, Um Ara granites, south Eastern Desert, Egypt.ORE GEOLOGY REVIEWS,35(3-4),436-446.
MLA El-Naby, Hamdy H. Abd."High and low temperature alteration of uranium and thorium minerals, Um Ara granites, south Eastern Desert, Egypt".ORE GEOLOGY REVIEWS 35.3-4(2009):436-446.
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