3D Gravity Inversion for Mineral Exploration Over Southern Green-stone-Belts of Ethiopia
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Date
2022-03
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Addis Ababa University
Abstract
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.
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Keywords
Inversion, gravity anomaly, Tikhonov regularization, density contrast