Geochemical Exploration for Gold Deposits in the Egyptian Nubian Shield
摘要
Gold Exploration in the Egyptian Nubian Shield began since the Predynastic time using “geologic” rather than “geochemical” tools. Recently, geochemical exploration techniques are involved in discovering many gold and other ore deposits all over the world. The fast development of advanced geochemical techniques and the rapid progress of computer-aided statistical tools and data processing models have led to a remarkable development in this field. Gold, because of its unique nature and behavior represents a great challenge for exploration geochemists in both reconnaissance and detailed stages of any lithochemical survey. This chapter aims at shedding light on some of the more advanced techniques that could enhance the efficiency of gold exploration in the Egyptian Nubian Shield. In Reconnaissance survey, new sampling procedures (e.g. Bulk Leach Extractable Gold “BLEG”) and advanced statistical techniques (e.g. fractal modeling) may improve this efficiency. The concentration-area (C-A) and concentration-number (C-N) fractal models are the most commonly used ones for stream sediment data interpretation. Applying the C-N fractal model on the stream sediments data set in the Sukari drainage system revealed that weak and moderate gold anomalies can be more clearly displayed by the fractal geochemical anomaly maps which can be correlated very well with the mineral potential maps constructed from the geochemical mineralization probability index. In detailed survey, using advanced statistical techniques (e.g. log-transformation data as centered log ratios and isometric log ratios), and new parameters (e.g. enrichment factor “EF”, ore forming index “YQ”) can lead to more accurate results and reliable interpretation of primary geochemical haloes. The enrichment factor associations in combination with the factor analysis associations were used to follow the dispersion and interpret the behavior of trace elements around the auriferous zones in the Sukari gold mine area. It was found that Mo and Cu are more enriched in the upper dispersion subzones, while W and Zn are more enriched in the lower subzones. This dispersion pattern can help locate mineralized zones in future drilling programs. Alteration zones, defined by specific alteration minerals, which surround many gold deposits and occurrences, are considered by some studies as new targets for gold exploration. The carbonate-sericite zones can be suggested as the most favorable zones for gold precipitation. In many recent studies, remote sensing techniques are combined with field and petrographic data to identify and delineate mineralized alteration zones. However, because of the challenges that face achieving this target, it is recommended to combine geochemical exploration techniques along with field data in combination with remote sensing and geophysical exploration programs in order to obtain optimum results and reliable evaluation of mineralized alteration zones.