| Botswana is located in the southern part of the African continent, there are several huge, superhuge copper-nickel, platinum, chrome, gold, diamond ore concentration areas in this country and its surroundings. The regional geology and mineralization conditions are advantageous in eastern Botswana. Three of the most important metallogenic tectonic units in southern Africa:Zimbabwe craton, Kaapvaal craton,and the Limpopo mobile belt,extend through eastern Botswana, which created an excellent mineralization tectonic condition in eastern Botswana.There are three copper-nickel mineralization intensive areas,Selebi-Phikwe, Matsitama and Selkirk in Zimbabwe craton and Limpopo mobile belt in eastern Botswana, and more than 40 copper-nickel deposits(points) has been found. There are lots of quartz-vein-type and shear-zone-type gold deposits associated with Archean greenstone in Zimbabwe Craton at Southeastern Francistown. Tati gold mineralization concentration area, where gold deposits(points) are up to more than 100, has been discovered. Francistown, located in the binding site between the Zimbabwe Craton and the Limpopo mobile belt. Zimbabwe craton contains 50% greenstone and most of the area has low degree of metal mineral exploration, but also a large area of mafic-ultramafic rocks are covered. This area is potential for copper-nickel and gold prospecting.Due to less exposed bed rocks and mineralization informations but well developed soil in the area, the author apply 1:50,000 soil geochemical prospecting methods to study the potential of copper, nickel and gold. The anomaly thresholds were calculated by traditional statistical data processing methods and Surfer trend surface methods, then the anomalies were delimited. Selected the anomalies by sorting them after counting their NAP, intensity, contrast. To verify the anomalies, we carried out geology, geophysical and geochemical comprehensive sections, with some trenches to expose the source of geological anomalies. Finally, the targets were selected after analysing comparatively and evaluating comprehensively.The results showed that:1. Comparing the content of each element in the soil of the region with that in the upper continental crust, it showed that: Au, Sb and Ti enriched, Zn significantly depleted, and other elements showed no obvious enrichment and depletion. Differentiation is characterized by: Au, As distribution is extremely uneven, which is a strong-differentiation-class; Cu, Pb is uneven distribution,which is a differentiation-class; Sb, Co, Cr, Ni, V, Zn shows uniform distribution,which is a weak-differentiation-class; and content distribution of Ti is even, and there no significant differentiation.2. The geochemical elements were classified to Co-Cu-Ni-Ti-V-Zn and As-Sb by factor analysis and cluster analysis. Co-Cu-Ni-Ti-V-Zn combination might reflect the abnormal area may be amphibolite and serpentine which were formed by metamorphism of original basic-ultrabasic rock formation, while As-Sb combination is two cryogenic elements, reflecting the abnormal area may the presence of quartz veins or shear zones associated with gold, silver and other alteration.3. Delineating 17 geochemical anomalies,including 1 Grade A2-2,1 Grade A3-2, 3 Grade B1,5 Grade B1,4 Grade B1 and 3 Grade C geochemical anomalies; Delineating 5 prospecting targets including 2 Grade Ⅰ, 0 Grade Ⅱand 3 Grade Ⅲ prospecting targets. Selecting one prospecting targets.4. The method 1: 50000 soil geochemical survey is suitable for semi-arid steppe landscape area in Central district of Botswana and, the results showed that the method delineated geochemical anomalies highly accurate and effective, and can achieve well results. |
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