Nasser L. El Agami, El Khedr H. Ibrahim, and Hatem H. Odah

Paleomagnetic and Geologic inferences, and probable origin of the Mn-Fe ore of Um Bogma SW Sinai, Egypt
Nasser L. El Agami, El Khedr H. Ibrahim¹, and Hatem H. Odah²

Nuclear Materials Authority, Cairo, ¹Dept. Geology, Fac. Sciences, Mansoura Univ.,
²National Inst. Astronomy and Geophysics, Helwan, Egypt

Paleomagnetic, mineral and geochemical study is carried out on the Um Bogma area, Egypt. Oriented samples were collected from 26 sites in the Mn-Fe ore and hosting rocks of Um Bogma Fm (Lower Carboniferous), and the overlying sandstone of Abu Thora Fm (Lower Carboniferous). The paleomagnetic pole determined from the characteristic remnant magnetization of 20 sites from Um Bogma Fm is located at Lat. = 22^oS; Long. = 97^oE (Dp = 3.9, Dm = 7.4).

This pole position falls close to the Carboniferous poles of Africa suggesting that the Mn-Fe ore could have been deposited during the Carboniferous time. Furthermore, the paleolatitude determined for these rocks, based on the mean paleomagnetic inclination, suggests that the ore was deposited where the area of study was situated at latitude 10^oS of the equator (i.e. at tropical weather conditions).

The minerals and chemistry show that the ore is enriched with Na, K, Ca, Mg, Sr, Co and Ni indicating that the ore is probably of sedimentary marine origin. Whereas the enrichment of ore samples with hydrothermal elements (As, Zn, Cu, Pb, V, W, and F) is restricted to the faulted areas indicating a later phase of hydrothermal activity affected the ore.

Abu Thora sandstone gave a mean paleomagnetic direction of
Dec. = 326^o, Inc. = 42^o, K = 19.3;

95 = 17.9^owhich yields a paleomagnetic pole position at
Lat. = 59^o; Long. = 302^o (Dp = 13.5, Dm = 22).

This magnetization is significantly different from that of the Mn-Fe ore and hosting rocks. It is believed that this remnant magnetization is related to the red pigmentation of the rock. A Cretaceous age is assigned for this remnance. It is suggested that this porous sandstone acquired its magnetization later after its deposition, more probably by diagenetic chemical processes.