Ra's Abdah of the north Eastern Desert of Egypt:the role of granitic dykes in the formation of radioactive mineralization,evidenced by zircon morphology and chemistry  

作　　者：Ali A.Omran Osama K.Dessouky 

机构地区：[1]Nuclear Materials Authority,P.O.Box 530,El Maadi,Cairo,Egypt

出　　处：《Acta Geochimica》2016年第4期368-380,共13页地球化学学报（英文）

摘　　要：Syenogranitic dykes in the north of Egypt's Eastern Desert are of geological and economic interest because of the presence of magmatic and supergene enrichment of radioactive mineralization. Zircon crystal morphology within the syenogranitic dykes allows precise definition of sub-alkaline series granites and crystallized at mean temperature of about 637 °C. The growth pattern of the zircons suggest magmatic and hydrothermal origins of radioactive mineralization. Hydrothermal processes are responsible for the formation of significant zircon overgrowth; high U-zircon margins might have occurred contemporaneously with the emplacement of syenogranitic dykes which show anomalous uranium(e U) and thorium(e Th) contents of up to 1386 and 7330 ppm, respectively.Zircon chemistry revealed a relative increase of Hf consistent with decreasing Zr content, suggesting the replacement of Zr by Hf during hydrothermal activity.Visible uranium mineralization is present and recognized by the presence of uranophane and autunite.Syenogranitic dykes in the north of Egypt＇s Eastern Desert are of geological and economic interest because of the presence of magmatic and supergene enrichment of radioactive mineralization. Zircon crystal morphology within the syenogranitic dykes allows precise definition of sub-alkaline series granites and crystallized at mean temperature of about 637 ;C. The growth pattern of the zircons suggest magmatic and hydrothermal origins of radioactive mineralization. Hydrothermal processes are responsible for the formation of significant zircon over- growth; high U-zircon margins might have occurred con- temporaneously with the emplacement of syenogranitic dykes which show anomalous uranium （eU） and thorium （eTh） contents of up to 1386 and 7330 ppm, respectively. Zircon chemistry revealed a relative increase of Hf consistent with decreasing Zr content, suggesting the replacement of Zr by Hf during hydrothermal activity. Visible uranium mineralization is present and recognized by the presence of uranophane and autunite.

关 键 词：Syenogranitic dykes ZIRCON Morphology Typology Uranium EGYPT 

分 类 号：P619.1[天文地球—矿床学] P588.121[天文地球—地质学]