Mining

No single global standard governs refuge bay design, and the collieries surveyed differ widely in construction, location, equipment and operating practice, which made ranking them impractical. Areas needing attention were identified in design, construction and maintenance of the facilities that keep people alive until rescue, drawn against local law and overseas practice.

Mapping abandoned, inaccessible bord and pillar workings comes down to two options: borehole deployed laser or sonar scanning, or sensors carried in by unmanned vehicles. Drone mounted laser scanning for air filled voids and sonar carried by small submersibles for flooded workings were judged the most promising, but intrinsic safety, deployment and the risk of losing equipment still favour borehole methods for occasional use.

Dust masks worn by load haul dump operators passed 200 mg of filter loading in an average of 1.7 hours, and continuous miner, shuttle car and roofbolt operators reached the same point within two to five hours. Every mask failed laboratory fit testing. An eight hour service life is too long.

Government and industry aeromagnetic data over the Witbank Coalfield were merged into one set of maps and GIS compatible files, and roughly 1200 dyke traces were interpreted from them. Purchase of a 200 m line spacing government survey removed the need for infill flying. One participating company valued advance knowledge of a single underground dyke at about R15 million.

Employee share ownership participation schemes are presented as a route to spreading mining wealth more widely after apartheid. They differ from profit sharing and pension arrangements in holding only the employer's own equity and in enlarging the company's capacity to borrow. Acceptance of such schemes in the South African mining industry was tested through an attitude survey of workers.

Dolerites in the study area differ in mineral content, geometry, thickness, grain size and degree of alteration. Plagioclase textures indicate fractionation at different depths in the crust for the Witbank and Sasolburg intrusions, and the olivine content points to separate magma sources for two of the sills. Fine crystalline dolerite, including chilled margins and bifurcations, alters most readily.

Computational fluid dynamics, checked against underground measurements, mapped ventilation flow and methane concentration around continuous miner headings for straights and splits, single and double scrubbers, side and straight scrubber discharges, jet fans, brattices and force columns. It showed the earlier physical test work cannot predict contaminant flow for larger machines or altered scrubber layouts.

South African underground sections average about 60 000 t a month, against 130 000 to 160 000 t for single pass bolter miner units on continuous haulage, while the better sections target 1.4 to 1.6 Mt a year. Australian longwalls deliver 5 to 7 Mt a year from one face, compared with 3 to 5 Mt at the two local wall operations.

Finite element simulation reproduced the rapid collapse of bord and pillar workings in the 2 Seam at a Witbank colliery, showing that progressive pillar deterioration triggers snap through of a strong sandstone plate in the overburden. Too little was known about the chosen collapse to back out a real pillar safety factor, so the calibration goal was not met.

Sets out the steps to establish a small scale coal mine in South Africa, from mineral rights and regulatory approvals through finance, mining and processing choices, marketing, and environmental management and closure. The information a new entrant needs sits in many separate places, so the guideline draws it together from practitioners rather than from any single published source.

Testing of 28 coal and coal-shale samples showed the coals to be more liable to spontaneous combustion than the shales, though reactive coal-shales still self-heat and pyrite in them speeds the process. Higher carbon, moisture, hydrogen, volatile matter and nitrogen with lower ash all raised proneness to self-heating, so proximate and ultimate analysis can serve as a screening tool.