Soils represent the weathered derivative of the underlying geology of every area. It is also a key tool in determining the geochemical dispersion of a target area for any mineral commodity sort out in exploration works.
The usefulness of magnetic intensity (Mag. Int.) mapping of the soils cannot be overemphasized especially in areas of scares iron formation outcrops which we find ourselves here in GSW2.
In this respect time has been taken out to analyze the magnetic intensity of the soils picked up during the field mapping activity in GSW2 target area of the Gbarnga Project. Figure 1 shows the point data of the magnetic intensity of soil picked up in the field from block one to block five. The data has been symbolized with soil of high magnetic intensity (MIH) having the biggest red circles up to soils with no magnetic intensity is having the smallest blue circles.
Fig. 1 Soil Magnetic Intensity Map in point data for GSW2
This information together with the contour map for the area have provided the bases for the formation of a Soil Magnetic Intensity Map (SMIM) displayed in figure 2. An observation can be made with soils of high magnetic intensity contoured red, medium magnetic intensity have been contoured orange and so forth. The north west of block one is seen to have some high magnetic intensity of the soil, areas around line 8 depicts some high magnetic intensity zones. Block five which is in the north eastern part of the map also has a good indication of a high magnetic area. This is in mountain Tumuye adjacent Siake’s town.
Fig. 2 Soil Magnetic Intensity Map for GSW2
Figure 3 displays an overlay of iron formation picked up during field mapping, mostly floats have been symbolized and placed on this soil magnetic intensity map to create and Iron Ore Zone Confidence Map in figure 4. This basically describes the degree of certainty of determining that an area has iron ore and the confidence attached to it. In other words the map provides first-hand information of probable iron ore zones.
Fig. 3. An overlay of IF on Soil Magnetic Intensity Map.
Fig. 4 Iron Ore Zone Confidence Levels
Obviously not all iron ore have the magnetic property and an area with iron formation outcrop has the highest confidence but in situations where there are no outcrops of iron then alternative means must be improvised as such, therefore three confidence levels have been proposed; High Confidence, Medium Confidence and Low Confidence.
High Confidence areas consist of the following:
High Soil Mag. Int. __High IF Mag. Int.
High Soil Mag. Int. __Medium IF Mag. Int.
Medium Soil Mag. Int. ___High IF Mag. Int.
Medium Confidence areas consist of the following:
Medium Soil Mag. Int. __Medium IF Mag. Int.
Medium Soil Mag. Int. _Low IF Mag. Int.
Low Soil Mag. Int. High IF Mag. Int.
Low Confidence areas consist of the following:
Low Soil Mag. Int. ___Low IF Mag. Int.
Low Soil Mag. Int. ___No IF Mag. Int. for
No Soil Mag. Int. ___Low to Medium IF Mag. Int.
This is a general observation from field experience even though exceptions are inevitable. For example I have observed areas like line 16 with a ferricrete dominated ground that has no magnetic attraction both for soil and rock on the surface but have iron ore underneath. Such trenches were proposed based on the continuing trend of iron ore from the south-west. These proposals are also based on a brownish red or reddish brown soil colour derived from the weathering of iron related formations. Areas with grey soil colour derived from the mechanical weathering of felsic material even with high magnetic intensity of IF floats are less likely to have iron ore as experience from the field has shown to date.
It is worth mentioning that a high percentage of ferricretes observed in block one are as a result of lateritization of the IF around and hence used to compliment the maps in figures 2 and 3.
Conclusion
With the scarcity of outcrops of iron formation in the project area, the influence of soils cannot be overemphasized in narrowing down targets for further exploration work.
This report aims to bring to light a thematic layer which is the Soil Magnetic Intensity Map to compliment the geological map as well as to give a first-hand target areas for further work.
A combination of Soil Magnetic Intensity Map and an Iron Formation Magnetic Intensity Map can provide a degree of certainty of favourable iron ore zones in a way to also narrow down targets for exploration.