ORIGIN OF Mn-Fe ORE BEARING RADIOACTIVE MINERALS AT UM BOGMA AREA, SOUTHWESTERN SINAI, EGYPT

The studied Mn-Fe ore deposits always tend to occupy a particular stratigraphic horizon, representing
the lower member of Um Bogma Formation which belongs to the Lower Carboniferous. Mn-Fe ore
deposits at Um Bogma area do not show the uniform characteristics of beds either in thickness or in lateral
continuity. In some occurrences, the ore bodies are present as sills, veins, fracture filling and also found on
the normal fault plane. All of these field criteria reveal hydrothermal origin of Mn-Fe ore deposits at Um
Bogma area. Mineralogically, kaolinite mineral is recorded in the studied Mn-Fe ore deposits in the four
localities, also Hausmanite and manganite detected in some localities (Allouga and Um Bogma) for the first
time indicating hydrothermal origin. The suggestion of hydrothermal origin is further supported by the
enrichment of Ba, Zn, Pb, As, U, V, Cu, and Sr, and depletion in Na, Mg, K, Ca and Ni in the studied Mn-Fe
ore deposits. The studied Mn-Fe ore deposits show lowΣ REEs contents, enrichment in LREEs relative to
HREEs and strong negative Ce anomalies. Also, all of these geochemical data confirm the hydrothermal
origin. In many localities manganese-iron ore bodies have spots reflecting high radioactivity reaches
up to 527 ppm of eU. The average of eU/eTh ratio for the studied samples of Mn-Fe ore deposits of the
four localities ranges between 4.0 up to 5.6 provide hydrothermal origin or may be later hydrothermal
enrichment of the manganese ore. Sayrite, thorite and uranothorite represents the radioactive minerals
detected in the studied Mn-Fe ore. Pinakiolite, rinmanite, turquoise, aheylite and gold also detected as
accessory minerals.