In February 2015 Ohorongo Cement (Pty) LTD and AEL Namibia embarked on an emulsion test trial project for both cost savings and reduction of manual labour to be measured and agreed, focused on increasing the drill and blast efficiencies and potentially changing to a new explosive at Ohorongo Cement quarry. The Ohorongo cement quarry operations are located approximately 45km north of Otavi in the central northern part of Namibia. Ohorongo Cement’s quarry currently averages around 400 000m3 of raw material per annum and projected an increase in production of about 500 000m3 at the end of 2017.
Prior to the commencement of the project, a site meeting was held to discuss the drilling and blasting (D&B) designs of the current practices at Ohorongo cement. AEL Namibia made recommendations on how to improve D&B efficiencies for the long term as well as to reduce manual labour on their current blast practises.
AEL Namibia provided a full Prime. Load. Tie-in and shoot (PLTs) service to Ohorongo cement to introduce the new explosives and accessories to be used for the trial blast. A bench of 43 holes was prepared and charged with sP200 eco emulsion and a total of 18866 BCM was blasted at a powder factor of 0.46kg/m3.
The following accessories were used for the trial blast:
Multi sPD 25m/500ms
Trunk Line 6m/17ms
Trunk Line 6m/42ms
Instantaneous electric Detonator (IeD)
400g Pentolite Booster OD 53mm in hole
The ground conditions of the prepared bench were in a good condition and easily accessible with a repump MMu. The following blast design was used as the holes had been drilled for an ANFeX design prior to the blast.
All holes were sleeved using 150mm tubing at 150microns thickness to prevent emulsion leaking away from the blast holes. The AEL team consistently monitored the cup samples to ensure the density stayed within specification due to the hole depth of 25m of which the diameter was only 95mm.
A cup sample of 1.04g/cc was required to achieve a 1.20g/cc average in hole density. The final toe density around the booster was calculated to be 1.27g/cc to ensure full detonation of the explosives column.
AEL performed well with the assistance from the production team of Ohorongo Cement.
The use of sleeves proved to be a tough battle as sharp rocks kept on damaging the sleeves inside the hole, due to the significant deviation and drilling angle of 80 degrees. The use of a 95mm hole at a depth of 25m in soft rock has proven it difficult to drill a proper pattern where the toe burden and spacing deviates significantly from the surface burden and spacing.
The blast was successful and a lot of knowledge was shared with the production team that was led by Rassie shilongo of Ohorongo Cement. The Customer was pleased with AEL's expertise and services and has requested to sign a 3 year exclusive supply contract.
AEL has offered the surface Blasting Competency course to the customer to enhance the skills of their production team.
The AEL team was led by Gunther Doll – Operations Manager and Henry Oswald –Field service superintendent.