Geochemistry of economic heavy minerals from rosetta black sand of Egypt

الملخص EN

The potential heavy minerals content of the black–sand resources in Rosetta is investigated using optical microscopy, X-ray diffraction, scanning electron microscope, electron-microprobe analysis and inductively coupled plasma-mass spectrometry.

The separation of individual minerals was done by wet-gravity and applying magnetic and electric approaches.

The composition and morphology of the studied heavy minerals such as zircon, monazite, garnet, magnetite, limonite and rutile are compared with their equivalents in the Nile sources to elucidate their fate during the long transportation.

Shukri's samples of the Nile sediments that were collected and studied during the mid-twentieth Century are adopted for this comparison.

Generally, mineral grains turn to be polished and free of contamination upon long transportation while others are entirely lost before reaching the influx.

Even the ultra-stable minerals such as zircon and monazite experienced some changes in their chemical composition during transportation.

The REE geochemistry suggests that the coarse grained zircon was possibly derived from highly fractionated and altered pegmatite rocks of White Nile proximity while the fine grained variety was derived from the Ethiopian hinterlands.

Two monazite varieties are distinguished, namely ; Ce-monazite and Th-monazite, however, the extreme Eu deficiency (ΔEu= <0.1) is used to assign derivation from highly fractionated felsic sources.

Garnet belongs essentially to alamandine variety is derived from metamorphic rocks such as the prevailing two mica schist of White Nile provenance.

The opaque minerals ; magnetite, ilmenite and rutile have nearly flat chondrite-normalized REE patterns but with slight enrichment in LREE.

These minerals are good indicators of the volcanic source of the Ethiopian plateau.

Few gold grains have been detected in the high grade cassiterite concentrate with average concentration of 7780 ppb Au.

The radioactivity in the studied black sands is essentially attributed to both uranium and thorium series mostly related to monazite, zircon, garnet and ilmenite.