Browsing by Author "Girum, Ashenafi"

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    3D Gravity Inversion for Mineral Exploration Over Southern Green-stone-Belts of Ethiopia
    (Addis Ababa University, 2022-03) Girum, Ashenafi; Tulu, Besha (PhD)
    Mainly this study aimed to investigate subsurface geology of the southern green stone mineralization zone for evaluation of gravity inversion is how effectively detecting high-density mineralization. Throughout the project, three main tasks have done: the first task was carrying out necessary correction for observed gravity data. Under this stage three main outputs were obtained: Bouguer gravity anomaly, regional Bouguer anomaly and residual Bouguer anomaly. The target information is represented by residual anomaly therefore it is became the final data for inversion process. The second task was minimizing Tikhonov’s cost function and carrying out inversion with the help of a conjugate gradient algorithm after formulated sensitivity matrix. The interpretation process was the last step of the work. The results obtained from the inversion process are demonstrated in two forms: the first one was a horizontal slice that illustrated the trend of mineralization in a horizontal plane and the second was density contrast model in a vertical plane that illustrated at four different lines of cross-section. In the horizontal density contrast model, the pixels value of high-density contrast under mineralization zone revealed 76.8% of pixels made a good agreement with the mineralization history of the target region. In addition, 90.3% of high-density contrast agreed with the location of metallic minerals in the region. In contrast, very low-density contrast in the region scored 3.77%. Therefore the inverted density contrast model well demonstrated the signature of mineralization in the target region. The vertical slice of the density contrast model indicated the depth condition of the high anomalous density region. Thus cross-section profile 1 up to 4 maximum depth and percentage of high density contrast above 600m depth are 1309.464m, 1089.866m, 847.72m, 661.0338m and 81.5%, 72%, 86.3%, 99.1% respectively. The vertical patterns of high-density contrast are correlated with the information obtained from a borehole at the mineralization zone. From such results and validation, I concluded: gravity anomaly inversion is a good tool to detect the position, depth extent, and the trend of the significant anomalous region.