干旱区生态环境知识资源中心(Arid): Rare metal-bearing pegmatites from the Southeastern Desert of Egypt: Geology, geochemical characteristics, and petrogenesis

Arid

DOI	10.1007/s11631-007-0008-8
	Rare metal-bearing pegmatites from the Southeastern Desert of Egypt: Geology, geochemical characteristics, and petrogenesis
	Saleh, Gehad M.
通讯作者	Saleh, GM
来源期刊	ACTA GEOCHIMICA
ISSN	2096-0956
EISSN	2365-7499
出版年	2007
卷号	26 期号:1 页码:8-22
英文摘要	The pegmatite province of the Southeastern Desert (SED) is part of a pegmatite district that extends from Egypt (extends to 1200 km(2)). Rare metal pegmatites are divided into (1) unzoned, Sn-mineralized; (2) zoned Li, Nb, Ta and Be-bearing; and (3) pegmatites and pegmatites containing colored, gem-quality tourmaline. The Rb/Sr data reflect a crustal origin for the rare metal pegmatites and indicate that the original SED magma was generated during the peak of regional metamorphism and predates the intrusion of post-tectonic leucogranites. These bodies developed an early border zone consisting of coarse to very coarse muscovite+quartz+alkali feldspar, followed by an intermediate zone of dominant quartz+feldspar+muscovite rock. Garnet, tourmaline, beryl, galena, pyrite, amblygonite, apatite and monazite are rare accessories in both zones. Cassiterite tends to concentrate in replacement zones and along fractures in albite+quartz+muscovite-rich portions. The highest concentrations of cassiterite occur in irregular greisenized zones which consist dominantly of micaceous aggregates of green Li-rich muscovite, quartz, albite and coarse-grained cassiterite. The different metasomatic post-solidification alterations include sodic and potassic metasomatism, greisenization and tourmalinization. Geochemically, the pegmatite-generating granites have a metaluminous composition, showing a differentiation trend from coarse-grained, unfractionated plagioclase-rich granite towards highly fractionated fine- to medium-grained, local albite-rich rock. Economically important ore minerals introduced by volatile-rich, rare metal-bearing fluids, either primarily or during the breakdown of the primary mineral assemblages, are niobium-tantalum oxides, Sn-oxides (cassiterite), Li-silicates (petalite, spodumene, euctyptite, and pollucite), Li-phosphates (amblygonite, montebrasite and lithopilite) and minor REE-minerals (Hfzircon, monazite, xenotime, thorian, loparite and yttrio-fluorite). The pollucite is typically associated with spodumene, petalite, amblygonite, quartz and feldspar. The primary pollucite has Si/Al (at) ratios of 2.53-2.65 and CRK of 79.582.2. Thorian loparite is essentially a member of the loparite (NaLREETi2O6)-lueshite (NaNbO3)-ThTi2O6-ThNb4O12 quaternary system with low or negligible contents of other end-member compositions. The mineral compositionally evolved from niobian loparite to niobian thorian and thorian loparite gave rise to ceriobetafite and belyankinite with high Th02 contents. Thorian loparite is metamict or partly metamict and upon heating regains a structure close to that of synthetic loparite NaLaTi2O6.
英文关键词	rare metal-bearing pegmatite geology geochemistry petrogenesis Egypt
类型	Article
语种	英语
收录类别	ESCI
WOS记录号	WOS:000218257700002
WOS类目	Geochemistry & Geophysics
WOS研究方向	Geochemistry & Geophysics
资源类型	期刊论文
条目标识符	http://119.78.100.177/qdio/handle/2XILL650/328915
作者单位	[Saleh, Gehad M.] Nucl Mat Author, POB 530, Cairo, Egypt
推荐引用方式 GB/T 7714	Saleh, Gehad M.. Rare metal-bearing pegmatites from the Southeastern Desert of Egypt: Geology, geochemical characteristics, and petrogenesis[J],2007,26(1):8-22.
APA	Saleh, Gehad M..(2007).Rare metal-bearing pegmatites from the Southeastern Desert of Egypt: Geology, geochemical characteristics, and petrogenesis.ACTA GEOCHIMICA,26(1),8-22.
MLA	Saleh, Gehad M.."Rare metal-bearing pegmatites from the Southeastern Desert of Egypt: Geology, geochemical characteristics, and petrogenesis".ACTA GEOCHIMICA 26.1(2007):8-22.

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