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Abstract
The Egyptian black sand deposits are discontinuously distributed along the northern Coastal Plain of the Nile Delta and Sinai Peninsula i.e. in the coastal stretch between Abu Qir to the west and Rafah to the east. These deposits contain strategic and economic minerals that include ilmenite, magnetite, garnet, zircon, rutile and monazite, in addition to leucoxene. These minerals are useful for nuclear, metallurgical and engineering industries.
The studied area is located after a perpendicular distance of ½ km from the mediterranean coast, east of Rosetta distributary mouth by about 8 km, and cover (2.5Km2). The area was evaluated for a depth of one meter and to a depth of 5 meters, using a 200 m X 100 m grid pattern.
Using the same grid pattern, the sampled locations were radiometrically surveyed by GS 512 gamma rays spectrometer to establish an approach for quantifying all or some of the individual economic minerals in the studied beach sands; especially some of its individual economic radioactive minerals (zircon and monazite).
Using a definite mineralogical analysis procedure program, the various heavy mineral contents in the different collected samples were calculated. The calculated total reserve of the economic minerals in the studied area reaches up to 164628.173 tons in the top meter and 516874.124 tons in the upper five meters. The calculated individual economic minerals reserves; expressed in thousands tons, for the evaluated drilled top meter area are as follows: ilmenite, 89.06; magnetite, 62.01; garnet, 3.59; leucoxene, 0.59; rutile, 2.68; zircon, 6.27 and monazite, 0.42. In case of the drilled five meters, the reserves are as follows: ilmenite, 303.07; magnetite, 161.82; garnet, 9.84; leucoxene, 5.30; rutile, 12.43; zircon, 24.42 and monazite, 0.04 .
Using both of wet gravity concentration, low and high intensity magnetic separation and high- tension electrostatic separation techniques, each of the individual six economic minerals and also leucoxene can be obtained in a high – grade concentrate with accepted grades and recoveries.
There are two types of the Egyptian beach leucoxene; the non – magnetic and the magnetic varieties. The non – magnetic leucoxene can be also termed secondary rutile and have the same magnetic and electrical characteristics as rutile. Hence, most of the non – magnetic leucoxene grained are contained associated with rutile in the final high – grade rutile concentrate.
The magnetic leucoxene varieties are weakly paramagnetic in comparision with rutile and non – magnetic leucoxene, then most of magnetic leucoxene can be separated in an individual magnetic fraction during the magnetic refining of the bulk rutile concentrate. Both hematite and chromite are relatively more magnetic than magnetic leucoxene.
Using the binocular microscope, high purified different leucoxene grain varieties were picked and collected according to their colours and magnetic susceptibilities. The grains were investigated using (ESEM). The obtained results reveal an agreement between the alteration extent of ilmenite grains and their colours, where high degrees of alteration exist in the relatively lighter coloured grains and vice-versa. The various tints of colours surrounging most of these grains were analyzed from rim to core across the grain; it was detected that the extent of leucoxenization process change from place to other along the same grains. However, most of leucoxenized ilmenite grains revealed the enrichment of TiO2 and decreasing in Fe2O3. Some MnO was lost during the alteration of ilmenite into pseudorutile and the rest was lost during the subsequent alteration to rutile. MgO shows a similar behavior.
Most of the mineralogical characteristics; physical and chemical properties, of the other economic minerals which include magnetite, ilmenite, garnet, zircon, rutile and monazite were also investigated.
Magnetite is considered of titanomagnetite type, it includes up to18 % TiO2 .
Ilmenite contains a considerable amount of Fe2O3 and lower amount of TiO2 (46.24 %).
Garnet minerals include alamandine, pyrope, grossularite and spessartine.
Zircon grains have several shapes, colours and inclusions.
The Egyptian beach rutile contains a relatively greater content of TiO2 (98.5% TiO2).
Monazite is considered an important source for REES, Th and U.