Geology of the Structurally Controlled Quartz Vein Gold Mineralization in the Dikko Area, Part of Zungeru—Minna—Birnin Gwari Schist Belt, NW Nigeria

Dikko area, Niger State, North Central Nigeria falls within the Pan-African thermo-tectonic event which occurred in Nigeria as in other parts of West Africa with widespread effect on the mineralization of rejuvenated basement and geosynclinal trough deposits. The Pan-African Belt in Nigeria forms part of the Benin-Nigeria (Dahomeyan) shield which is regarded as the southern prolongation of the circumcratonic Pan-African belt of the West African Craton. Structurally controlled, gold-bearing quartz veins were measured and studied in the area from an extensive geological ground investigation. Field and petrographical studies indicate that the Neoproterozoic rocks constitute gneisses, amphibolite schist, amphibolites and migmatites. The amphibolites are intruded by pegmatites. The associated quartz veins are generally concordant with the main N-S regional structural trend. The lithological and structural studies carried out in these areas have demonstrated the relationship between structures and mineralization and/or lithology. The main characteristics of the gold mineralization in the area appear to indicate hydrothermal mineralization in connection with shear zones. This study allows us to predict that quartz veins in the amphibolite can be mined at a profit and a detailed geochemical and resource valuation needs to be carried out for the Au and associated Galena and Ag mineralization to fully exploit their economic potential.

The Eocene Bryozoans of Bekrit-Timahdite Formation, Middle-Atlas, Morocco: Taxonomy, Paleoenvironments and Paleoclimates Implications

Located in the North-West of the African continent, the Moroccan Middle Atlas constitutes an intra-continental chain within the Atlas domain. It is known by several global geological events such as the Paleocene-Eocene crisis during the Paleogene, which corresponds to one of the hottest periods on earth with Paleocene-Eocene thermal maximum (PETM). A taxonomic study carried out on the carbonate deposits of the Bekrit-Timahdite Formation from three sections of the Bekrit syncline allowed the identification of 5 species of the Cheilostome and Cyclostome Bryozoans (Cellaria rigida, Cellaria sinuosa, Aimulosia lamellosa, Heteropora and Osthimosia) in bioclastic limestones, nodular limestones, marly and sandy limestones. The interest of Bryozoans as indicators of paleoenvironments and paleoclimates was assessed by examining current communities, in terms of depth evolution as richness and abundance, distribution of taxonomic categories zoarium types, and zooidal morphology. The depositional environment analysis of Bryozoans showed a shallow marine carbonate platform with low sedimentation energy where is registered a relatively warm paleoclimate.

Late Cretaceous-Paleogene Formation of the Bekrit Syncline, Middle Atlas, Morocco: Sedimentology, Geochemistry, Palynology and Paleoenvironments

Globally, the Paleogene period experienced several events marking the Paleocene-Eocene transition which is especially to one of the hottest periods that the Earth has ever known (Paleocene-Eocene Thermal Maximum, PETM), followed by the biological crisis that affected benthic foraminifera. The Bekrit Syncline, subject of this study, shows three Formations of range from the Cretaceous to the Eocene ages (the El Koubbat, Irbzer and Bekrit-Timahdite Formations). Sedimentological, palynological and geochemical analyses of collected samples, in the Bekrit syncline, were studied to determine the paleogeographic and paleoenvironmental conditions of the Middle Atlas. The carbonate rocks were analyzed by microscopic study and geochemical analysis by X-ray Fluorescence (XF) and Inductively Coupled Plasma Spectrometry (ICP). The results obtained highlight the sedimentary events that took place during the Paleogene. Thus, the Maastrichtian is characterized by a closed euxinic marine environment shared by a more open and oxidizing environment. On the other hand, the Paleocene was a restricted marine environment with evaporitic sedimentation, while the Eocene sees the installation of a carbonate platform with a bioclastic Shoal.

Effect evaluation of shale types on hydrocarbon potential using well logs and crossplot approach,Halewah oilfield,Sab'atayn Basin,Yemen

Log-analysts typically distinguish three types of shale distribution in clastic reservoirs,that is,laminated,dispersed and structural distribution,which tend to influence the effective porosity and permeability of reservoirs.The Alif Member is made up of sandstone interbedded with some shale,with shale dominating on top and at the bottom.In sedimentary formations,the gamma ray log normally reflects the shale content.The gamma ray log and neutron-density porosity crossplot is used to estimate a reservoir's shale volume(Vsh),according to which the Alif Member is divided into three zones.In addition,shale types are recognized by neutron-density porosity crossplot,and the correlation coefficients of gamma ray log-based Vsh and neutron-density porosity-based Vsh are suggested to be reliable.The Vsh and shale types of the three zones are compared against the reservoir's potential to yield hydrocarbons.The major oil intervals mainly concentrate in shaly sand and sandstone zones of dispersed and laminated shale types.The third zone,the lowermost interval,contains pure shale of laminated type and is considered out of reservoir standards in hydrocarbon production due to its excessive shale volume.Quantitative assessment of shale type distribution and Vsh by crossplot approach could not furnish correct information to evaluate massive shale intervals.

Engineering and Tectonic Study of Rocks Discontinuities in the Proposed Abo-Hederya Quarry Site, Missan SE Iraq

A detailed field survey of discontinuity (fractures) was carried out in the proposed Abo-Hederya Quarry Site, 70 km east Missan city, south-east of Iraq, where Al-Mukdadiya Formation (Upper Miocene-Pliocene) is exposed. The discontinuity survey was carried out in 10 stations covering the study area. At each station notes were collected about beds (lithology, thickness and orientation) and discontinuities (orientation, density, spacing, persistence and aperture). The slope stability analysis suggests that there is no real hazard area that could affect the quarry in future. Tectonic analysis demonstrates that tension fractures are common in the study area, while shear fractures (okl, hko, hol and hkl) are the less. The maximum principal stress direction in the study area is N (15 - 40) E, which is compatible with the regional tectonic stress in the area.

Zircon Trace Element Constraints on the Evolution of the Paleoproterozoic Birimian Granitoids of the West African Craton(Ghana)

The Paleoproterozoie Birimian granitoids of the West African Craton （WAC） in the northwestern part of Ghana, have been studied for their zircon trace elements concentrations to infer the source characteristics, origin, and magmatic evolution. The zircons in the granitoids have Th/U ratios ranging from 0.03 to 1.55, and display depleted light rare earth elements 0LREE） and enriched heavy rare earth elements （HREE） contents, characterized by pronounced positive to negative anomalies of Eu （Eu/Eu＊=0.14-0.98 and 1.01-6.06, respectively） and Ce （Ce/Ce＊=0.08-0.98 and 1.02-116, respectively）, which may imply that they were derived from both magmatic and hydrothermal sources. The geochemical plots of U/Yb vs. Y and Hf, the positive correlation between Hf and the other high field strength elements 0tFSE） and high rare earth elements （REE） contents, with enrichment in Ce and depletion in Eu, indicate that the granitoids possibly formed from partial melting of the crust. The trace elements characteristics （i.e., wide range of Hf, Ce/Ce＊, Th/U and Zr/Hf values） of the zircons suggest that crystallization of the magma occurred under variable oxidation states, which spanned over a longer period, implying that our data corroborate interpretations from studies of whole-rock geochemistry and geochronology on the granitoids of northwestern Ghana. This further indicates that the evolution of the Birimian granitoids in this part of the WAC occurred earlier than what had been reported in the literature.