Figure 1. a. Regional locality map and b. Simplified subsurface geologic map of the Witwatersrand basin. The Carbon Leader is located within the Upper Witwatersrand Supergroup
Figure 2a. Virgin rock temperature distribution in the Witwatersrand gold mining arc (after Jones and Bottomley, 1986)
Figure 2b. Profile of three mines from Western Deep Levels Ltd. located in the Carletonville gold field. Samples examined for this proposal are from mine shaft #1, level 109. Gray arrows schematically indicate water circulation from the base of shaft to level 109.
Figure 3. Maximum likelihood trees based on full 16S rRNA gene sequencing of clone material. (a) Tree showing sample Bulk R 2B clones corresponding to sulfate-reducing and other mixotrophic bacteria that can reduce iron. (b) Tree showing gene sequence of clones from the Carbon Leader A (CL-A) and B (CL-B) samples. The 16S rRNA sequence for the dominant clones from the carbon leader are the most similar to cyannobacteria in the RDP data base, although the similarity is not high.
Figure 4. a. Phospholipid fatty acid (PLFA) concentrations in the quartzite, carbon leader, biofilm (rock slime) and formation water sample from Western Deep Levels. The concentration of PLFA are a direct measure of biomass and exhibit high variability in the rock samples (10^5 to 10^7). The water sample yield a low biomass (1 x 10^5 cells/g). b. The mole% of the different lipid fraction indicates that the carbon leader either that it is contaminated by fungal spores or cyannobacteria. The rock slime yielded a composition that suggest that sulfate reducing bacteria are the dominant active bacteria.
Figure 5. The Hg porosimetry data for the quartzite adjacent to the carbon leader exhibits a maximum pore throat diameter of .8 microns, just large enough for bacteria to slide through. The low permeability and low porosity indicate that ground water velocities and oxygen diffusion are limited.
Figure 7. Transmission electron micrograph of Thermus bacteria isolated from Witswatersand gold mine. These bacteria were capable of reducing Fe oxides (fine-grained material around the cells). This photo was taken on positively stained samples (with OsO4 and uranium acetate) by Hailiang Dong and Gordon Southam at Northern Arizona University.
Figure 8. A similar transmission electron micrograph of Thermus but taken on negatively stained sample (uranium acetate). It shows the whole body of one bacterium which is dividing into two smaller ones.
Figure 9. Water encountered during cover drilling of access tunnel in West Driefontein mine (Shaft #6) at 2.7 kilometers below the surface (kmbls). During drilling, a 1 meter long casing is set with valves to protective against flooding in case water is encountered. Joost Hoek for scale. This water is anaerobic and sulfide producing and has a temperature of approximately 45°C.
Figure 10. These older boreholes at West Driefontein (shaft #6-2.7 kmbls.) are still emanating water. Characteristic dark material below holes may represent residual drilling lubricant. Orangish discoloration appears to be Fe oxidation. Bright buff color is cement. Quartz veins are readily visible in surrounding rock.
Figure 11. Fractures are visible in West Driefontein access tunnels. Walls of access tunnels are characteristically mottled with black spots, which we suspect represents condensation of diesel fumes from trolley. Compare this to photos of actively mined stopes.
Figure 12. Mineralized fracture in West Driefontein (shaft #5-1.8 kmbls.). Mineralization (white band on corner of fracture surface is younger than red paint used to mark rock surface during drilling. Note black mottling on white paint at bottom of photo. Potentially older mineralization may be present on fracture plane. We need to determine this.
Figure 13. Carbon leader in West Driefontein (shaft #5). This is about 1 cm in width and very soft and greasy.
Figure 14. Weeping borehole in East Driefontein (Shaft #5-level 46). The borehole extends approximately 120 meters into the volcanic rock of the Ventersdorp lavas. This casing is approximately 1 meter long. The flud dripping out is highly saline. Orangish discoloration may represent Fe-oxides forming. Glove for scale.
Figure 15. Carbon leader at East Driefontein mine (shaft #5-level 48). Thin carbon leader is primarily confined between conglomerate foot wall and quartzite hanging wall. Bands of pyrite obvious in conglomerate as are other layers of organic carbon.