الفهرس | Only 14 pages are availabe for public view |
Abstract Banded Iron Formations (BIFs) are of economic potential, as they host the world’s largest iron ore and much gold deposits. The Umm Nar BIF is one of the biggest arc sedimentary rock units in the Precambrian sequence of the Eastern Desert of Egypt. It was strongly influenced by multi-deformation of folding and faulting during or after the closure of the Mozambique Ocean (650- 620 Ma). The present study includes integration of data from geochemical and geophysical exploration. Detailed gravity and magnetic surveys were carried out in the Umm Nar BIFs using CG5 gravimeter and Overhauser magnetometer, respectively. Gravity exploration was suitable for detecting the Umm Nar iron ore due to its high density contrast with the schist country rocks. The magnetic method was suitable also for locating buried magnetite ore body because of its high magnetic susceptibility. In addition, gravity and magnetic surveys are considered to be accurate, less-expensive, non-destructive environmentally exploring tools, and have a wide coverage. Geosoft Oasis Montaj 7.1 program, Sufer10 program, and Matlab codes were used for processing, adjusting and interpreting both gravity and magnetic data. The gravity data were corrected for the common gravity corrections (drift, topography, free air and Bouguer). The magnetic data, on the other hand, were corrected for the diurnal variations and reduced to the Northern magnetic pole. Qualitatively, both residual gravity anomaly and magnetic to pole maps refer to two main sets of faults directed NE-SW and E-W. Both maps identify high anomaly areas matching the exposed iron bands reflecting their subsurface SW extension. Depth of the source body was estimated to 100 - 400 meter using Euler deconvolution method, and up to 350 meter using Downward continuation. Combination of the two analyzed interpretation methods (Tikhonov (1968) regularized downward continuation and Derivative Euler Deconvolution) could effectively help in the estimation of the depths to the centres of researched near surface gravity and magnetic sources. Abstract Furthermore, geochemical analyses of 20 positioned surface samples were performed using X-Ray Fluorescence (XRF). These analyses showed high concentration of iron reaching to 75% in the area of high gravity and magnetic anomaly. Iso-chemical maps of the fluid mobile elements demonstrate well matching with the Ag concentration, concluding the role of the metamorphic fluids in ore shaping potential. The Pearson linear correlation matrices divide chemical elements into six associations: i) Fe, Co, Ni, Ag, Nb, Sb, I, Ce, W, As, ii) Si, iii) Na, Al, Mg, P, K, Rb, Y, Ba, Ti, Zr , iv) Mn, Cu, Mo, V, Sr, Br ± Pb, v) Ca, Sc, vi) Cr, Se. Geochemical mapping constrains structural control of metals with NW-SE and WNW-ESE faulting. |