Underground Trials of Seismic-counter and Goafing Characteristics in Pillar Extraction

Electrical and electromagnetic ground surveys were run over a Waterberg profile with borehole logs and three dimensional seismic data as control, to test whether cheaper methods can match seismic reflection for locating coal and faults. Resistivity tomography at two electrode spacings, frequency and time domain electromagnetics, controlled source audio magnetotellurics and magnetics were all acquired. Results are preliminary.

Tonnage estimates for the remaining low phosphorus resource could not be produced, because the phosphorus analyses supplied by mining companies did not state what had been measured. Distribution trends were still mapped. Coal at or below 0.010 per cent phosphorus is widespread in the Witbank Coalfield, restricted to the far northwestern Highveld, and follows a northwest to southeast band in eastern Ermelo.

Ground based radar mapped rehabilitation soil profiles well enough to replace much of the auger sampling normally needed, and a 100 MHz system picked out anomalies at about 5 to 6 m depth that were likely old mining voids and related subsidence. Penetration below roughly 6 m needs lower frequencies, which cost resolution and require larger antennas.

Hydrogen for biological sulphate removal can be generated on site by electrolysis more cheaply than it can be bought. Stainless steel electrodes in acid mine drainage gave hydrogen at about a third of the bought in price while oxidising ferrous iron to ferric, which helps downstream treatment. Iron and zinc electrodes dissolved too quickly to be viable.