The Northam mine site is located in an area of probable maximum intensity of MMV as per the Modified Mercalli Scale and the Munich Re world map of hazards. Although the factory mutual data sheets indicate that a major earthquake could occur every 40 to 70 years, documented history indicates no record of earthquakes in the area of the mine.
Northam is the deepest platinum mine in the world. Underground workings are characterized by particularly high virgin rock temperatures (VRT) that demand considerable refrigeration capacity.
Underground mining focuses on the exploitation of platinum group metal ores by means of traditional drill and blast narrow tabular reef mining methods. A standard breast mining layout is used at Northam. The vertical interval (distance) between levels is 63 metres. With the orebody dipping at 20°, this provides a raise length of 180 metres allowing for six panels of 30 metres each. Strike gullies are inclined at 10° above strike. Dip gullies handle the ore transported via the strike gullies to the three orepasses, all of which are fitted with radial-door control chutes. Ore is transported to the main shaft ore passes by battery powered locomotives (locos) pulling spans of eight hoppers.
Mining is successfully conducted using a breast-stoping method, employing hydropowered rock drills.Water-jets and scrapers are used to clean the stopes. Broken ore is transported to a conventional ore-pass system, with separate rock handling facilities for Merensky reef, UG2 reef and waste.
The underground workings are accessed from a twin shaft system. No 1 shaft extends to 12 level and No 2 shaft serves workings down to 8 level. The shafts are 90 metres apart and are interconnected at an intermediate pump chamber (IPC) at 1 019 metres below surface, and also on levels 4, 6, 7, 8 and 9. Workings below 12 level are serviced by a decline access way, designed to accommodate both people and materials, and equipped with a conveyor belt system that transports the broken rock.
Shaft technical specifications | | One shaft | Two shaft |
| Diameter | 8,5m | 9,15m with upcast segment |
| Winding depth (m) | 2 063 | 1 755 |
| No of compartments | 8 | 4 |
| Ventilation | Downcast | Downcast/Upcast |
| Number of rock winders | 2 x double drum | 1 x double drum |
| Skips per hour | 2 x 15 | 17 |
| Average hoisting hours per day | 19 | 19 |
| Rock hoisting capacity (%) | 64 | 36 |
| Hoisting days per month | 24 | 24 |
| Average tons per month | 165 000 | 90 000 |
| Reef hoisting capacity in event of disruption in opposite shaft | 83% | 47% |
| Man winders | 1 x double drum | 1 x cage – c/weight |
| Service winder | 1 | 1 |
| Hydropower columns 300 nominal bore (NB) | 1 (another is at 50% completion) | 1 |
| Compressed air columns | 1 x 200 NB | 1 x 250 NB |
| Electrical supply | 8-13 level, IPC pumps, transfer pumps | 2-7 level, IPC pumps |
| Pump columns | 2 x 400 NB from transfer to IPC & IPC to surface | 1 x 300 NB from IPC to surface |
| Backfill | - | 8 x columns and 20 ranges distributed to working places |
http://www.northam.co.za/business/mining_method.asp
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