The Masimong mines are situated in the Free State of South Africa and are part of the Harmony gold mining company. Harmony is the fifth largest gold producing company in the world. Masimong 5 has gold reserves of 2,129,000 oz (proven and probable).
The Masimong shafts exhibit intense faulting due to a number of north-south trending faults parallel to the Homestead fault in the west. Reef dips are mainly to the south-east, varying from 5 to 35 degrees. Masimong 5 Mine is currently mining Basal Reef as well as the B Reef. The B Reef is characterised by complex
sediment logically-controlled gold mineralisation within a wide east-west trending channel, which cuts through the lease
area. Within this channel, very high grade gravel bars containing abundant
kerosene and visible gold were deposited.
Masimong 5 is currently being actively mined for ore whilst Masimong 4 is being used as a waste shaft.
Waste and reef, are transported on the same belt, at different times during the day and night.
Previous to the RF Tags OREtrak system being implemented at Masimong a ‘belt and magnet’ system was used to try and prevent cross tramming and to gain more control underground. The ‘belt and magnet’ system proved ineffective as metal washers were frequently buried in the stuff and would go through the system undetected. Where these washers were detected manually compiling reports with the findings has proved to be very labour intensive. Additionally, the mine managers had no idea of the length of time it was taking to transport ore to the surface.
Before embarking on the project a full site survey was carried out by RF Tags to analyse the material flows and check the operation in detail. This included checking the communications and IT infrastructure as well as possible reader placements with Masimong engineers.
Implementation and Operation
As part of OREtrak the ‘production control’ office at Masimong received an ‘issuing reader’. This was essentially a short range radio frequency reader which was able to read the preprogrammed unique tag number. Once the tag was read by the issuing reader the RF Tags SQL database was updated automatically with the specific tag number.
Against the tag number in the database the following information was input
- the stope location where the tag would be placed
- a time and date
- a production team reference
Tag Issuing program
A reader with two antennas was installed on the belt sampler. The antennas were positioned 500mm above the belt to ensure that they were not hit by larger rocks. The antennas were attached to the reader and orientated into the optimum position for reading the tags on the belt. The reader communicated, in this implementation via a telephone line, to the OREtrak database in the production control office.
Antennas on the belt
On passing the reader/antennas on the belt the tags were activated and communicated their tag number to the reader. The reader in turn communicated the reader number, the tag number and the date and time back to the OREtrak database.
‘Read’ results program
Where cross tramming was found to be occurring the specific tag record on the OREtrak screen changed from black to red. This meant that corrective action could be taken quickly to resurrect the situation. In practice, at Masimong, the production team leaders responsible were disciplined at a later date.
At Masimong daily and weekly exception reports from OREtrak were sent to managers. Masimong found it also useful to report on which tags had not yet passed the readers i.e. were still in working stopes. Masimong believe that 40% of the total tags seeded in the stopes have now surfaced and the rest are still underground. This knowledge allowed a full evaluation of the efficiency of the individual production teams with corrective action put into place where necessary.
The system has been running since April 2006 and the managers at Masimong now have a heavy reliance on OREtrak to give them knowledge and therefore control of what is happening underground.
The Masimong results after OREtrak was implemented were excellent with a reduction of reef loss on the waste belt from 1 gram per tonne to 0.6 grams per tonne.
With the continual use of the OREtrak system Masimong expect to gain further loss reductions down to 0.4 of a gram reef loss on the waste belt in the next few months. Masimong believe that the tags are currently 100% reliable i.e. all tags that have surfaced have been read by the RF readers.