First Blast at Ohorongo Cement Quarry

On Tuesday 23rd of March, Ohorongo Cement conducted its first blast in the Sargberg quarry. Erastus Shilongo, blasting supervisor of Ohorongo Cement, ignited the 2 150kg water gel explosives distributed over 144 holes. The blast prepares the first 600 square meters of quarry ground for mining.

While the Ohorongo Cement plant is still in the construction phase and marketing of the first cement is only scheduled for January 2011, Tuesday’s blast distinguishes the quarry as the first link to become operational in the productive chain of the entire Ohorongo Cement plant. This timely start of mining is necessary to give access to all the different mineral qualities which will be mined at commissioning of the plant later in theyear.

During normal operations, about two blasts are conducted per week. The precise composition and quantity of material to be mined and delivered to the plant is determined by the quality department and communicated to the quarry supervisor, where the mineral composition of the materials is assessed from the drill cuttings of the blast holes.

Over the 1 500 meter long quarry, all components of cement - limestone, marl, shale and calcrete – can be mined in their different layers. About 75% of mined material consists of limestone, while the remainder is made up of shale, marl and calcrete.

As one of the first Ohorongo blasters who received the Namibian surface blasting ticket, Shilongo is excited to have been the one setting of f the blast. ‘I am proud to be a member of the team opening the quarry - together with my colleagues Gottfried Geist and the others. This quarry will not only outlast us who work here today , but will even outlive my children – and probably their children too!’

During quarry development and first mining stages, the shoulder of the quarry will have a height of 12.5 meters. At a later stage, the quarry will be deepened to 25 meters. When fully operational, about 5 500 tonnes of raw material will be mined daily from the quarry. When the plant is in full production, the quarry staff will consist of 22 full time employees, of which nine people are already working in the quarry. The quarry staff receives practical on the job training by specialists flown in from Germany.

Besides Mr Shilongo, one further member of the quarry team has received the Namibian surface blasting ticket. Due to the design of the blast, the blast vibrations will be relatively low with no risk of damage or disturbance to surrounding farmsteads, roads or the railway line. Also, as Schwenk geologist Dr Markus Schauer assured us, the quarry lies in a geological syncline, insulated from the ground water bearing layers serving the region. No risk of groundwater contamination thus exists.

The quarry has a capacity to deliver 1 200 000 tonnes of raw material annually, which translates into 700 000 tonnes of high quality cement per annum. The proven resource will last for more than 300 years of operation, underlining that the Ohorongo plant is not a short term investment but will serve the Namibian building industry sustainably into the distant future. Consulting geologist Arno Günzel from Arnex Geological Services is pleased to have discovered and mapped this resource: ‘It is not every day that a geologist has the privilege to find a resource of this magnitude. Working for Ohorongo will always remain as one of my very good memories.’