الفهرس 
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Abstract
Extensive field and laboratory studies were carried out on the rocks of the unconformable contact zone between the Lower Carboniferous Adediya and Um Bogma formations as well as those of the latter rock unit in three stratigraphic sections in G. Um Hamd. A detailed geologic map of the study area was constructed. It revealed the presence of two major dip- slip and a number of minor faults. The sedimentary succession is intruded by basaltic dykes that are connected with the Tertiary volcanicity.
The contact zone consists of argillaceous rocks. The Um Bogma Formation could be subdivided into a lower siltstone- Fe, Mn ore member, a middle siltstone- mudstone- shale member and an upper dolostone- dolomitic limestone member. The argillaceous rocks in the succession are slightly calcareous, poorly- sorted and variably highly ferruginous; Fe- oxides have several modes of occurrence. Rocks of the contact zone are texturally classified as mudstone and sandy mudstone whereas those of the Um Bogma Formation are sandy siltstone, sandy mudstone, sandy claystone and muddy sandstone. On the other hand, the carbonates of the upper member of Um Bogma Formation are classified as microsparite, dolomitized microsparite, dolomitized sparite and dolomitized pel-oosparite.
The studied rocks consist of a large mineral assemblage made up of primary and secondary minerals that are allogenic and authigenic. They are non-radioactive, radioactive and U-, Th- and REEs- and base metals- bearing in addition to native gold and silver. The clay fractions of the argillaceous rocks consist of kaolinite and, in certain rock units, smaller proportions of montmorillonite- illite and/or chlorite- illite.
The geochemical characteristics of the studied rocks were investigated by determining the concentrations and behaviour of the major elements oxides, trace elements, REEs, base metals and total organic carbon. The obtained chemical data were normalized to the chondrite, UCC and PAAS and plotted on several variation diagrams. Also, these data were statistically treated in order to construct correlation matrices and elucidate a number of computational parameters. The results obtained were implemented to determine the distribution patterns, inter-relationships and degree of enrichment or depletion of all elements in the various rock units as well as the redox conditions in the depositional environments. In addition, the roles played by bacteria and fungi in the concentration and accumulation of some minerals and elements were assessed and documented.
Radioactivity varies markedly among the different rock units being highest in the rocks of the middle member of Um Bogma Formation followed by those of the contact zone. For all the argillaceous rocks, values of chemical U are higher than those of eU indicating U gain. The correlation matrices revealed that eU values have strong positive relationships with those of Uc, V, Ta and Nb and negative correlations with those of Fe2O3, Y and the REEs budget. Also, rocks of the Um Bogma Formation have relatively low values of the eTh/eU ratio and K content suggesting secondary U enrichment. Values of eU/eTh indicate U addition in the studied rocks except for those of the Adediya- Um Bogma contact zone and the upper member of Um Bogma Formation. The radioactivity equilibrium states for the various rocks and the type and amount of U migration were determined. In addition, the oxidation-reduction conditions in the depositional environments were assessed.
The studied argillaceous rocks were inherited from acidic to ultramafic igneous rocks and, to a much lesser extent, metamorphic and sedimentary rocks. Their clay mineral constituents are of mixed allogenic/ authigenic and primary/ secondary origin. The products of deep chemical weathering of source rocks were transported by rivers and streams of low to moderate strength. Deposition of the argillaceous sediments took place in various types of fluvial environments and, less commonly, littoral lakes, lagoons and swamps. Accumulation of sediments of the uppermost Adediya Formation was followed by a period of exposure and chemical weathering accompanied by active supergene processes. On the other hand, the carbonates were originally deposited as limestones in shallow agitated low intertidal environments that changed by time into a more quiet subtidal setting as a result of gradual sea transgression.
Diagenesis played a major role in modifying the original textural and compositional characteristics of the rocks. It involved compaction, cementation, alteration, replacement and dissolution. These post- depositional processes commenced during the mesogenetic (burial) stage and became more profound during epigenesis by the action of meteoric and underground waters as well as the hydrothermal solutions that are connected with the Tertiary volcanicity.
Keywords: Southwestern Sinai, G. Um Hamd, Paleozoic, Adediya Formation, Um Bogma Formation, argillaceous rocks, carbonates, petrography, mineralogy, geochemistry, radioactivity, REEs, base metals, gold, silver.