الفهرس 
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Abstract
Um Bogma manganese-iron deposit is a large stratiform manganese-iron oxide ore body contained in the marine carbonate rocks of west central Sinai, Egypt. The origin of these deposits is still a matter of controversybetween researchers, where some of them considered the ores to be of sedimentary origin, others supported the hydrothermal one. The present work aimed at to studying and identifying the geologic setting, mode of occurrence, mineralogy and geochemical factors controlling the distribution of manganese and associated metals in the manganese-iron ores to recognize their origin.
Image processing techniques were applied using the digital ETM+ data of Landsat 7 to construct a detailed geological map. The techniques include; construction of an optimum Landsat ETM+ false color composite image, histogram equalization of Landsat ETM+-data, band ratio of Landsat ETM+-data, color composite ETM+ band ratio images and principal component analysis of ETM + data.
The outcropping rocks belong to the Paleozoic age and unconformably overly the Precambrian basement rocks, but are overlain by basaltic sheets of probable Permo-Triassic age. The Paleozoic sequence attains a thickness ranges from 160 to 365m.They are divided into three sedimentary sequences; the Lower Sandstones (Sarabit El Khadim, Abu Hamata and Adedia Formation), the Carboniferous Limestone Series (Um Bogma Formation) and the Upper Sandstone Series (Abu Thora Formation).
The Lower Sandstone Series unconformably overlies a flat, weathered plain surface of the crystalline basement rocks, and is overlain by the Carboniferous Limestone Series. The series consists of alternating sequence of sandstone and shales. Impregnations of manganese minerals are common in its lower part, while some copper mineralization appears in its upper part. The Carboniferous Limestone Series (Um Bogma Formation) unconformably overlies Adedia Formation and is unconformably overlain by Abu Thora Formation. It consists of hard crystalline dolomite with some limestone and marl layers. The Upper Sandstone Series (Abu Thora Formation) consists of shale, siltstone, white sandstone, kaolin, clay and carbonaceous shale and covered by basaltic sheets.
One of the main goals of the present study is to extract the major and minor structural lineaments by applying some enhancement techniques on ETM+ satellite images. Statistical parameters were analyzed using SPSS software. The directional analysis of the azimuth frequency of structure lineaments revealed that the NNE, NE and NW are the most extensive trends. On contrary, structural lineaments of E-W and WNW-ESE are considered to be of less abundance and have low length extension. The northern part of the study area is characterized by low density and intersection of structural lineaments and remarkable increase was recorded in central and southern parts. The northern part of Um Bogma displays majority zones, while in western and eastern zones are localized in small spots. The NNE-SSW trend has the maximum abundance of majority zones allover Um Bogma area, followed by NE-SW structural trends. The NNW and NW majority zones are mainly concentrated in the northern sector of study area, but the NS zones are mainly concentrated in the western part of the area.
Factor analysis indicated the presence of significant correlation between NS and NNE (r= 0.66), where these two directions are tectonically related to the Gulf of Aqaba tectonic trend. NNE and NW trends have the highest standard deviation values due to the reactivated movements that resulted in the dispersion of fractures direction from the mean. On the other hand, the least reactive trends seem to have the lowest standard deviation.
Manganese, iron and copper mineralization was reported in the fine-grained sandstone and shaly sandstones of Abu Hamata Formation in the form of spots, patches and along the shale fissile planes and also within the sandstones of Adedia Formation. However, the main manganese-iron ore were recorded in many morphological shapes as lenticular bodies, sheets, encrustation and filling the fractures and vugs in Um Bogma Formation especially in the Dolomite Member and the Marly dolomite Member associated with green copper carbonate staining. The ore consists of series of disconnected lenses of about 2.0 to 3.0 meter thick. In many occurrences, the manganese lenses are completely separated from the iron ore and occasionally the manganese lenses are surrounded by iron ores or change vertically into more iron-rich ore. The ore also occur as alternating sheets of manganese and iron oxides parallel to the bedding planes. The presence of manganese oxides as fracture fillings and filling the vugs in the dolomite beds may reveals that the manganese oxides were formed from hydrothermal solution
The manganese-iron ores at Um Bogma area are chemically classified into three types depending on their contents of manganese and iron oxides and on the MnO/Fe2O3 ratios:
1- Type 1 (Mn-rich ore) characterized by high contents of MnO (average 78.51 wt %.), Al2O3, Cu, Zn, Pb, Co, Ni, Ba, Zr and low contents of low Fe2O3 (average 2.46 wt %),SiO2, TiO2, V, Sr and Nb.
2- Type 2 (Mn-Fe rich ore) characterized by more or less equal contents of both MnO and Fe2O3. This type is relatively enriched with SO3, Zn, Sr and depleted with Al2O3, TiO2, Co, Ni and Cu and have intermediate concentration of SiO2, Cr, V and Zr.
3- Type 3 (Fe- rich ore) characterized by high contents of Fe2O3 (average 84.99 wt %.), SiO2, TiO2, V, Cr, Co, Ni, Nb and low contents of MnO (average 1.33 wt %), Al2O3, SO3, Cu Sr, Ba, Pb and Zr.
The correlation coefficients indicated the presence of negative correlation between MnO and Fe2O3 (r=-0.94) suggests their precipitation under different environmental conditions. Ba and Cu show positive correlation coefficients with MnO and negative correlation with Fe2O3 reflecting their selective adsorption on the manganese oxides rather than iron oxides and may explain that manganese is derived from a hydrothermal source. SiO2 shows a positive correlation with Fe2O3 and negatively correlated with MnO which attributed to the presence of detrital quartz grains in the iron ores rather than manganese ores. The strong positive correlation coefficients among Co, Ni, Cu, Pb, Zn indicate their formation by hydrothermal solutions.
Factor analysis of the major oxides and trace elements data revealed the following findings:
1- Factor one is highly positively correlated with Fe2O3, SiO2, TiO2, V, Cr and Co reflecting the adsorption of Co, V and Cr on the iron oxides and the clastic contribution of Si, Ti and V during deposition. It is also negatively correlated with MnO2 and Ba reflecting the adsorption of Ba on manganese oxides.
2- Factor two is highly positively correlated with Al2O3, K2O, P2O5, Co, Cu, Y, La, Pb and slightly positively correlated with MnO2 reflects the adsorption of Co, Cu and Pb on the hydrous manganese oxides as well as the sedimentary contribution of Al2O3, K2O, P2O5, Y and La to mineralization.
3- Factor three is strongly positively correlated with MgO, CaO, Zn, Rb, Sr and Zr reflecting the presence of carbonate minerals.
Major and Trace element contents in the manganese-rich ore samples indicated that the manganese ores were formed in shallow marine depositional environment. The following results strongly support the hydrothermal origin of the ores:
1- The high Mn/Fe ratios (average 23.27).
2- The high Cu, Zn, Pb and Ni contents (average 1138ppm, 1211ppm, 125ppm, 133ppm respectively)
3- The low Al and Ti contents (average is 0.93 wt % and 0.05 wt % respectively).
4- The Co/Zn ratio (average 0.11) more or less around the Co/Zn ratio for hydrothermal manganese deposits (0.15).
5- High Ba contents (average 2435ppm).
6- Also, the hydrothermal character of Fe-Mn ores was clarified based on the Fe - Si×2 – Mn, Mn-Fe-(Co+Ni+Cu)×10, Co+Ni - Cu+Pb+V+Zn discrimination diagrams.