Application of Geophysical Exploration Methods in Mapping Gold Mineralisation Zones. Case Study: Makina Prospect in the Busia-kakamega Greenstone Belt, S.e. Uganda.

Abstract

The geophysical survey exploration programme in Makina was done as a follow up on gold in soil geochemical anomalies delineated by Mayfox Mining Company. The survey grid covered an area of approximately 10 square kilometers. This contained 60-line kilometers of ground magnetic survey and 42-line kilometers of gradient Induced polarization- Resistivity survey that was conducted in the project area. The aim of the geophysical surveys was to determine the extent of gold mineralization and its associated geological and structural controls. The Induced polarization, Resistivity and Magnetic surveys conducted in the project area have produced anomalies consistent with structural and lithological trends relevant to gold mineralization. The chargeability anomalies conform almost perfectly to the trends established from the soil geochemical anomalies. The combined interpretation of the resistivity and magnetic data reveals pertinent rheological variations, suggesting evidence of shear zones or fracture zones, typical of mineralization controls in the Busia-Kakamega greenstone belt. The geophysical maps produced have aided the interpretation of the local geological setting. Distinct lithological boundaries have been inferred and interpreted from analysis of these maps. High chargeability patterns appear to coincide with high magnetic anomalies, supporting the initial association of the area’s deposits with sulphide mineralization and more specifically iron sulphides like pyrite and pyrrhotite. Preliminary analysis of the integrated datasets shows the potential occurrence of mineralization hosted in two geological frameworks. First, there are indications that the Banded Iron formation hosts disseminated mineralization as well as in the accompanying minor shear and contact associated quartz veins and veinlets. The second class is linked to the almost North-South trending fault/fracture zones. The orientation of the latter classification shows resemblance to the Tira deposit. The two prospective target zones delineated in this project, warrant further exploration and are potentially future drill targets. Pole-Dipole IP/Resistivity surveys have been proposed to target the most prospective chargeability anomalies. The Pole-Dipole data will provide crucial subsurface information on the trend and continuity of the potential ore mineralization besides affirming the veracity of current postulations. The Pole-Dipole data, inversion models and pseudo-sections can then be used to generate drilling targets. For this project area, three initial survey profiles have iv been proposed along IP lines; L5200E, L600E and L7200N. The results of this project have emphasized the importance of integrating the IP/Resistivity technique and ground magnetics in gold exploration. Further, the results have shown how suitable the methods can be, especially in the search for potentially deep-lying ores and in the tropical regions, where weathering and leaching processes such as lateritization, may adversely influence soil geochemical surveys. The potential for the regional continuity of the mineralization is evident and intensified exploration works are required to unearth this potential further to the North and West of the survey area and. To the east of Tira and even across the border into Kenya, the grounds are mostly underexplored despite the evident geological potential posed by the rich yet structurally intricate Busia Kakamega-greenstone belt.