Analysis and mapping of soil geochemical anomalies: Implications for bedrock mapping and gold exploration in Giyani area, South Africa

• Soil geochemical data are useful for predicting underlying bedrock geology.
• Principal component analysis is a useful tool for predicting bedrock lithology.
• Soil geochemical data are useful for exploration of orogenic gold mineralisation in the Giyani, South Africa.
• Colour composite maps of PCs are used to discriminate between different bedrock geology.

Previous exploration activities in the Giyani greenstone belt (GGB) were guided by the availability of outcrops, particularly iron formation, as this rock was considered to be the main host rock for gold mineralisation in the belt, although the majority of the known prospects/deposits are hosted by mafic rocks. However, there is no reliable lithological map available for the GGB, because most of it is covered by regolith, and thus in the early 1990s most mining and exploration companies in the GGB have abandoned their work as they were discouraged by the scarcity of outcrops, the small sizes of existing deposits and the low gold prices at that time. In the present study, major and trace element geochemical data from a high-density soil geochemical survey (1 sample/km2) have been subjected to statistical and spatial analyses to support bedrock mapping and gold exploration. Maps are presented for major oxides, trace elements and selected respective ratio maps, and principal components (PC). The PC analysis was performed on clr-transformed data of selected trace elements known to be associated with gold mineralisation. The first six PCs explain about 78% of the total variance. PC4 representing Sb–As–Te–Cr–Au association best reflects the known gold mineralisation and was, therefore, used as a thematic layer. The information provided by various composite maps of different major/trace element data, as well as PC maps, has been used to produce an interpretive bedrock map outlining major lithological units in the study area. As gold mineralisation in the Giyani greenstone belt is hosted by certain known lithologies, the map is useful in indicating potential gold bearing areas.