الفهرس 
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Abstract
The present work is concerned with the mineralogy and geochemistry of Nusab El Balgum area. The
area is bounded by Latitudes 23o 15/ to 23o 20/ N and Longitudes 29o 15/ to 29o 20/ E and forms an
elongated body trending in the NNE-SSW.
Gabel Nusab El Balgum is located at the northern part of Bir Safsaf area southwestern Desert,
Egypt, covering about 40km2. The area consists mainly of sandstone (Devonian), volcanic rocks
(Permo- Triassic), altered granitic rocks and post granitic dykes. The altered granitic rocks
(silicified and kaolinized) are suffered from hydrothermal alteration and subjected to different
types of alteration (hematitization, carbonitization, kaolinization, sericitization and
silicification).
Petrographically; the volcanic rocks are classified into rhyolite, dacite and tuffs. The silicified
granite is characterized by complete absence of plagioclase where the potash feldspars and quartz
are the main constituents. Mafic minerals are mainly alkaline pyroxenes that intensively altered or
metasomatized by meteoric or hydrothermal solutions. The kaolinized granite is characterized by the
complete alteration of feldspars to sericite and kaolin. The studied dykes could be classified to
granitic dyke (slower cooling giving fine grains), rhyolitic dyke (rapid cooling giving very fine
crystals) and dacitic dyke (variable cooling and variable grain size). Veins are represented by
monomineralic rocks invading the granite and could be classified in this study to quartz vein (very
fine quartz) and jasper vein (cryptocrystalline silica).
Mineralogically; conglomerate is characterized by the presence of (REE silicate, monazite,
columbite, pyrite, nickel, barite, zircon,apatite, garnet and titanite), volcanic rocks and associated dykes contains
(REE silicate, cerite, fergusonite, columbite, gold, galena, atacamite, zircon, fluorite,
xenotime, apatite and garnet).
Thorite, uranophane, autunite, bastnaesite, parisite, allanite, REE silicate, fergusonite,
columbite, hydrothermal zircon, xenotime, ilmenorutile, gold, nickel, pyrite, galena, sphalerite,
barite, and atacamite are common in the silicified and kaolinized granites. Silicified granite has
average of rare metals more than kaolinized granite. The REE in Nusab El Balgum granites were
brought by hydrothermal fluids into rocks during alteration and may be precipitated in carbonate
minerals such as bastnaesite (LREE) (CO3) F and parisite Ca (LREE) 2(CO3)3F2. The mineralogical
studies confirm the presence of three mineralization stages, the earliest mineralization stage
(high temperature stage) is characterized by the formation of native Au associated with hypogene
rare metals (pyrite, galena, sphalerite and native Ni). The second stage (lower-temperature) is
characterized by the formation of supergene secondary minerals; uranium, barite and atacamite.
Third stage is related to carbonate facies formed after the oxide (supergene alteration).
Geochemically, the conglomerate reflects their deposition in semi-arid to semi-humid climatic
conditions and in passive margin. The studied Permo-Triassic volcanic rocks and associated dykes
are comenditic- pantelleritic in composition, equivalent to continental basalt and were generated
in extensional environment exhibiting within plate volcanism. All volcanic rocks show moderate
enrichment of most High field strength elements (HFSE) and depletion in Low field strength elements
(LFSE). The average of total rare earth elemental concentration of volcanic rocks and associated
dykes are (1483&1667 ppm) respectively, with Eu-anomaly (Eu/Eu* =0.2&0.18), and Ce anomaly (Ce/Ce*=0.87 &1.1). The calculated values of the tetrad effect range from 0.9 to 1.1 in volcanic rocks and from 1.03 to 1.5 in dykes.
The altered granites fall in argillic to sericitic facies (characterized by any member of the kaolinite group) and enriched in many large ion lithophile elements (LILE) and high field strength elements (HFSE) as compared with kaolinized granite. All granitic samples possess some A-type granitoid features and derived from continental crust or under plated crust. The altered granites are characterized by enrichment in LREEs (10852 & 341 ppm), depletion in HREEs (1186 &329 ppm), negative Eu* anomaly (0.19 & 2) in silicified and kaolinized granite respectively. The Chondrite-normalized REE patterns of the silicified and kaolinized granite show M-type tetrad effect. Rare earth in Nusab El Balgum altered granites are related to hydrothermal alteration during hydrothermal fluid–rock interaction.
Radioactivity: The silicified granite shows abnormal radioactivity more than kaolinized granite. The mineralizing solutions may be uranium bearing of hypogene and supergene origin fluids which percolate on the granites and leach of uranium. Then, mobilization of uranium within the granite, and deposition of uranium and thorium along the fractures where the planes of these structures provided easy channels for the passage of uranium-bearing solutions and suitable structural trap for radioactive minerals accumulations.
So it is recommended that the altered granites and post granitic dykes should be studied by underground geophysical techniques in order to detect and determine the extent of the underground source for mineralization.