Johannesburg - South Africa - AEL Mining Services, an international leader and innovator in blasting solutions, recently partnered with EBJ Mining Construction to successfully execute mechanised, inverse box hole blasting at Harmony Gold's Elandsrand Mine, which has resulted in increased safety and production.

Eugene Fouche, acting mine manager at Elandsrand Mine, comments, "In the past, we used long hole mechanical (raise boring) and short hole conventional development. With the increase in the reef development rate, this method proved to be slow and labour intensive, resulting in a backlog of box holes. We changed to a mechanised method, combining inverse box holes with drop raising.

"This new mechanised method", adds Fouche, “entails drilling the ore pass from the bottom of the rock upwards at an angle using an automatic drilling machine. This minimises the number of people physically involved in the drilling and blasting of the ore passes, resulting in increased safety of personnel."

Inverse box hole drilling also ensures a more accurate holing point without fracturing the rock, thereby reducing the chances of rock slips and rock-related injuries. “The current advance rate for conventional box holing is on average 1.2 m per day, compared to inverse blasting of 2m per day,” says Fouche

Elandsrand Mine has converted to the DigiShot range of electronic initiation systems supplied by AEL's sister company, DetNet, which eliminates the need for blast operators, thereby putting more men out of harm's way. Electronic detonators also ensure that the timing and precision of each blast is accurate.

The hole is blasted with a single blast up to 15m from the bottom up. The remainder of the ore pass is blasted from the top of the raise. An homogenous emulsion with glutinous properties is used to charge the hole, and ensure that the explosives do not fall out of the predrilled hole when initiating the blast.

Johan Fourie, Regional Manager at AEL comments on the blasting of the inverse drop raise hole, “With the traditional box hole development method, it would take approximately 12 days to advance 15 metres before loading and blasting the hole. This process could take longer in some of the older gold mines where reef exposure is minimal. With inverse drop raising, we are able to drill the whole length of the tunnel in six days and then blast on the seventh day, reducing the turnaround time from twelve to seven days”.

About Elandsrand Gold Mine

Elandsrand Mine straddles both Gauteng and North West Province, and is located near the town of Carletonville. The mine was acquired by Harmony in January 2001. The mine comprises a twin vertical and sub-vertical shaft system. The Elandsrand metallurgical plant treats ore from the Elandsrand shaft. The Elandsrand deepening project, which came into production in FY04, involved the development of a new mine beneath the original Elandsrand Mine. The project will target the southern, deeper portion of the higher-grade Ventersdorp Contact Reef pay shoot at depths of between 3000m and 3600m. The project was re-started by Harmony in FY01 following the acquisition of Elandsrand.

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